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USGS2019

Mapping irrigated cropland extent across the conterminous United States at 30 m resolution using a semi-automatic training approach on Google Earth Engine

Accurate and timely information on the distribution of irrigated croplands is crucial to research on agriculture, water availability, land use, and climate change. While agricultural land use has been well characterized, less attention has been paid specifically to croplands that are irrigated, in part due to the difficulty in mapping and distinguishing irrigation in satellite imagery. In this study, we developed a semi-automatic training approach to rapidly map irrigated croplands across the conterminous United States (CONUS) at 30 m resolution using Google Earth Engine. To resolve the issue of lacking nationwide training data, we generated two intermediate irrigation maps by segmenting Landsat-derived annual maximum greenness and enhanced vegetation index using county-level thresholds calibrated from an existing coarse resolution irrigation map. The resulting intermediate maps were then spatially filtered to provide a training data pool for most areas except for the upper midwestern states where we visually collected samples. We then used random samples extracted from the training pool along with remote sensing-derived features and climate variables to train ecoregion-stratified random forest classifiers for pixel-level classification. For ecoregions with a large training pool, the procedure of sample extraction, classifier training, and classification was conducted 10 times to obtain stable classification results. The resulting 2012 Landsat-based irrigation dataset (LANID) identified 23.3 million hectares of irrigated croplands in CONUS. A quantitative assessment of LANID showed superior accuracy to currently available maps, with a mean Kappa value of 0.88 (0.75–0.99), overall accuracy of 94% (87.5–99%), and producer’s and user’s accuracy of the irrigation class of 97.3% and 90.5%, respectively, at the aquifer level. Evaluation of feature importance indicated that Landsat-derived features played the primary role in classification in relatively arid regions while climate variables were important in the more humid eastern states. This methodology has the potential to produce annual irrigation maps for CONUS and provide insights into the field-level spatial and temporal aspects of irrigation.

conterminous United States↗

USGS2020

Conterminous United States land cover change patterns 2001–2016 from the 2016 National Land Cover Database

The 2016 National Land Cover Database (NLCD) product suite (available on www.mrlc.gov), includes Landsat-based, 30 m resolution products over the conterminous (CONUS) United States (U.S.) for land cover, urban imperviousness, and tree, shrub, herbaceous and bare ground fractional percentages. The release of NLCD 2016 provides important new information on land change patterns across CONUS from 2001-2016. For land cover, seven epochs were concurrently generated for years 2001, 2004, 2006, 2008, 2011, 2013, and 2016. Products reveal that land cover change is significant across most land cover classes and time periods. The land cover product was validated using existing reference data from the legacy NLCD 2011 accuracy assessment, applied to the 2011 epoch of the NLCD 2016 product line. The legacy and new NLCD 2011 overall accuracies were 82% and 83%, respectively, (standard error was 0.5%), demonstrating a small but significant increase in overall accuracy. Between 2001-2016, the CONUS landscape experienced significant change, with almost 8% of the landscape having experienced a land cover change at least once during this time. Nearly 50% of that change involves forest, driven by change agents of harvest, fire, disease and pests that resulted in an overall forest decline, including increasing fragmentation and loss of interior forest. Agricultural change represented 15.9% of the change, with total agricultural spatial extent showing only a slight increase of 4,778 km2, however there was a substantial decline (7.94%) in pasture/hay during this time, transitioning mostly to cultivated crop. Water and wetland change comprised 15.2% of change and represent highly dynamic land cover classes from epoch to epoch, heavily influenced by precipitation. Grass and shrub change comprise 14.5% of the total change, with most change resulting from fire. Developed change was the most persistent and permanent land change increase adding almost 29,000 km2 over 15 years (5.6% of total CONUS change), with southern states exhibiting expansion much faster than most of the northern states. Temporal rates of developed change increased in 2001-2006 at twice the rate of 2011-2016, reflecting a slowdown in CONUS economic activity. Future NLCD plans include increasing monitoring frequency, reducing latency time between satellite imaging and product delivery, improving accuracy and expanding the variety of products available in an integrated database.

ISPRS Journal of Photogrammetry and Remote Sensing↗

USGS2021

Remote sensing-based actual evapotranspiration assessment in a data-scarce area of Brazil: A case study of the Urucuia Aquifer System

The large groundwater reserves of the Urucuia Aquifer System (UAS) enabled agricultural development and economic growth in the western Bahia State, in northeastern Brazil. Over the last several years, concern has grown around the aquifer’s diminishing water levels, and water balance (WB) studies are in demand. Considering the lack of measured actual evapotranspiration (ET a ), a major component of the water cycle, this work uses the Operational Simplified Surface Energy Balance (SSEBop) model to estimate ET a , and compares it to basin-scale estimates from the Soil Moisture Accounting Procedure (SMAP) monthly model and from an annual WB closure method, based on gridded meteorological data and the Gravity Recovery and Climate Experiment (GRACE) product. Additionally, a comparative assessment of different versions of the SSEBop parameterization was performed. Moderate Resolution Imaging Spectroradiometer (MODIS) imagery was used to implement eight different versions of the SSEBop algorithm over the UAS between 2000 and 2013. SSEBop and SMAP ET a yielded similar seasonal patterns, with correlation coefficient (r) up to 0.65, mean difference (MD) of 0.8 mm/month and mean absolute difference (MAD) of 18.5 mm/month. Comparison of SSEBop annual ET a estimates to annual SMAP and WB closure estimates yielded low MD (12.1 and −7.3 mm/year, respectively) and MAD (82.5 and 82.8 mm/year, respectively), but also low r values (0.00 and 0.37, respectively). The comparison of the different SSEBop versions indicated the need to incorporate a calibration step of the aerodynamic heat resistance (r ah ) parameter. SSEBop results were also used for land cover and drought monitoring. Analysis indicates that agriculture, associated with an increasing trend of atmospheric evaporative demand, is responsible for the decrease in groundwater levels and streamflow in the studied time period.

Urucuia Aquifer System↗

USGS2004

Evaluation of land performance in Senegal using multi-temporal NDVI and rainfall series

Time series of rainfall data and normalized difference vegetation index (NDVI) were used to evaluate land cover performance in Senegal, Africa, for the period 1982–1997, including analysis of woodland/forest, agriculture, savanna, and steppe land cover types. A strong relationship exists between annual rainfall and season-integrated NDVI for all of Senegal ( r =0.74 to 0.90). For agriculture, savanna, and steppe areas, high positive correlations portray ‘normal’ land cover performance in relation to the rainfall/NDVI association. Regions of low correlation might indicate areas impacted by human influence. However, in the woodland/forest area, a negative or low correlation (with high NDVI) may reflect ‘normal’ land cover performance, due in part to the saturation effect of the rainfall/NDVI association. The analysis identified three areas of poor performance, where degradation has occurred over many years. Use of the ‘Standard Error of the Estimate’ provided essential information for detecting spatial anomalies associated with land degradation.

Journal of Arid Environments↗

USGS2008

Sensitivity of summer climate to anthropogenic land-cover change over the Greater Phoenix, AZ, region

This work evaluates the first-order effect of land-use/land-cover change (LULCC) on the summer climate of one of the nation's most rapidly expanding metropolitan complexes, the Greater Phoenix, AZ, region. High-resolution-2-km grid spacing-Regional Atmospheric Modeling System (RAMS) simulations of three "wet" and three "dry" summers were carried out for two different land-cover reconstructions for the region: a circa 1992 representation based on satellite observations, and a hypothetical land-cover scenario where the anthropogenic landscape of irrigated agriculture and urban pixels was replaced with current semi-natural vegetation. Model output is evaluated with respect to observed air temperature, dew point, and precipitation. Our results suggest that development of extensive irrigated agriculture adjacent to the urban area has dampened any regional-mean warming due to urbanization. Consistent with previous observationally based work, LULCC produces a systematic increase in precipitation to the north and east of the city, though only under dry conditions. This is due to a change in background atmospheric stability resulting from the advection of both warmth from the urban core and moisture from the irrigated area. ?? 2008 Elsevier Ltd. All rights reserved.

Journal of Arid Environments↗

USGS2004

Nitrate and herbicide loading in two groundwater basins of Illinois' sinkhole plain

This investigation was designed to estimate the mass loading of nitrate (NO3-) and herbicides in spring water discharging from groundwater basins in an agriculturally dominated, mantled karst terrain. The loading was normalized to land use and NO3- and herbicide losses were compared to estimated losses in other agricultural areas of the Midwestern USA. Our study area consisted of two large karst springs that drain two adjoining groundwater basins (total area of 37.7 km2) in southwestern Illinois' sinkhole plain, USA. The springs and stream that they form were monitored for almost 2 years. Nitrate-nitrogen (NO3-N) concentrations at three monitoring sites were almost always above the background concentration (1.9 mg/l). NO3-N concentrations at the two springs ranged from 1.08 to 6.08 with a median concentration of 3.61 mg/l. Atrazine and alachlor concentrations ranged from <0.01 to 34 ??g/l and <0.01 to 0.98 ??g/l, respectively, with median concentrations of 0.48 and 0.12 ??g/l, respectively. Approximately 100,000 kg/yr of NO3-N, 39 kg/yr of atrazine, and 2.8 kg/yr of alachlor were discharged from the two springs. Slightly more than half of the discharged NO3- came from background sources and most of the remainder probably came from fertilizer. This represents a 21-31% loss of fertilizer N from the groundwater basins. The pesticide losses were 3.8-5.8% of the applied atrazine, and 0.05-0.08% of the applied alachlor. The loss of atrazine adsorbed to the suspended solid fraction was about 2 kg/yr, only about 5% of the total mass of atrazine discharged from the springs. ?? 2004 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2006

Increasing streamflow and baseflow in Mississippi River since the 1940 s: Effect of land use change

A trend of increasing streamflow has been observed in the Mississippi River (MR) basin since the 1940 s as a result of increased precipitation. Herein we show that increasing MR flow is mainly in its baseflow as a result of land use change and accompanying agricultural activities that occurred in the MR basin during the last 60 years. Agricultural land use change in the MR basin has affected the basin-scale hydrology: more precipitation is being routed into streams as baseflow than stormflow since 1940 s. We explain that the conversion of perennial vegetation to seasonal row crops, especially soybeans, in the basin since 1940 s may have reduced evapotranspiration, increased groundwater recharge, and thus increased baseflow and streamflow. This explanation is supported with a data analysis of the annually and monthly flow rates at various river stations in the MR basin. Results from this study will help to direct our effort in managing land use and in reducing nutrient levels in MR and other major rivers since nutrient concentrations and loads carried by storm water and baseflow are different. ?? 2005 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2008

Tile drainage as karst: Conduit flow and diffuse flow in a tile-drained watershed

The similarity of tiled-drained watersheds to karst drainage basins can be used to improve understanding of watershed-scale nutrient losses from subsurface tile drainage networks. In this study, short-term variations in discharge and chemistry were examined from a tile outlet collecting subsurface tile flow from a 963 ha agricultural watershed. Study objectives were to apply analytical techniques from karst springs to tile discharge to evaluate water sources and estimate the loads of agricultural pollutants discharged from the tile with conduit, intermediate and diffuse flow regimes. A two-member mixing model using nitrate, chloride and specific conductance was used to distinguish rainwater versus groundwater inputs. Results indicated that groundwater comprised 75% of the discharge for a three-day storm period and rainwater was primarily concentrated during the hydrograph peak. A contrasting pattern of solute concentrations and export loads was observed in tile flow. During base flow periods, tile flow consisted of diffuse flow from groundwater sources and contained elevated levels of nitrate, chloride and specific conductance. During storm events, suspended solids and pollutants adhered to soil surfaces (phosphorus, ammonium and organic nitrogen) were concentrated and discharged during the rapid, conduit flow portion of the hydrograph. During a three-day period, conduit flow occurred for 5.6% of the time but accounted for 16.5% of the total flow. Nitrate and chloride were delivered primarily with diffuse flow (more than 70%), whereas 80-94% of total suspended sediment, phosphorus and ammonium were exported with conduit and intermediate flow regimes. Understanding the water sources contributing to tile drainage and the manner by which pollutant discharge occurs from these systems (conduit, intermediate or diffuse flow) may be useful for designing, implementing and evaluating non-point source reduction strategies in tile-drained landscapes. ?? 2007 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2008

Assessment of crop growth and soil water modules in SWAT2000 using extensive field experiment data in an irrigation district of the Yellow River Basin

SWAT, a physically-based, hydrological model simulates crop growth, soil water and groundwater movement, and transport of sediment and nutrients at both the process and watershed scales. While the different versions of SWAT have been widely used throughout the world for agricultural and water resources applications, little has been done to test the performance, variability, and transferability of the parameters in the crop growth, soil water, and groundwater modules in an integrated way with multiple sets of field experimental data at the process scale. Using an multiple years of field experimental data of winter wheat (Triticum aestivum L.) in the irrigation district of the Yellow River Basin, this paper assesses the performance of the plant-soil-groundwater modules and the variability and transferability of SWAT2000. Comparison of the simulated results by SWAT to the observations showed that SWAT performed quite unsatisfactorily in LAI predictions during the senescence stage, in yield predictions, and in soil-water estimation under dry soil-profile conditions. The unsatisfactory performance in LAI prediction might be attributed to over-simplified senescence modeling; in yield prediction to the improper computation of the harvest index; and in soil water under dry conditions to the exclusion of groundwater evaporation from the soil water balance in SWAT. In this paper, improvements in crop growth, soil water, and groundwater modules in SWAT were implemented. The saturated soil profile was coupled to the oscillating groundwater table. A variable evaporation coefficient taking into account soil water deficit index, groundwater depth, and crop root depth was used to replace the fixed coefficient in computing groundwater evaporation. The soil water balance included the groundwater evaporation. The modifications improved simulations of crop evapotranspiration and biomass as well as soil water dynamics under dry soil-profile conditions. The evaluation shows that the crop growth and soil water components of SWAT could be further refined to better simulate the hydrology of agricultural watersheds. ?? 2008 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2008

Application of multiple isotopic and geochemical tracers for investigation of recharge, salinization, and residence time of water in the Souss-Massa aquifer, southwest of Morocco

Groundwater and surface water in Souss-Massa basin in the west-southern part of Morocco is characterized by a large variation in salinity, up to levels of 37 g L-1. The high salinity coupled with groundwater level decline pose serious problems for current irrigation and domestic water supplies as well as future exploitation. A combined hydrogeologic and isotopic investigation using several chemical and isotopic tracers such as Br/Cl, ??18O, ??2H, 3H, 87Sr/86Sr, ??11B, and 14C was carried out in order to determine the sources of water recharge to the aquifer, the origin of salinity, and the residence time of water. Stable isotope, 3H and 14C data indicate that the high Atlas mountains in the northern margin of the Souss-Massa basin with high rainfall and low ??18O and ??2H values (-6 to -8??? and -36 to -50???) is currently constitute the major source of recharge to the Souss-Massa shallow aquifer, particularly along the eastern part of the basin. Localized stable isotope enrichments offset meteoric isotopic signature and are associated with high nitrate concentrations, which infer water recycling via water agricultural return flows. The 3H and 14C data suggest that the residence time of water in the western part of the basin is in the order of several thousands of years; hence old water is mined, particularly in the coastal areas. The multiple isotope analyses and chemical tracing of groundwater from the basin reveal that seawater intrusion is just one of multiple salinity sources that affect the quality of groundwater in the Souss-Massa aquifer. We differentiate between modern seawater intrusion, salinization by remnants of seawater entrapped in the middle Souss plains, recharge of nitrate-rich agricultural return flow, and dissolution of evaporate rocks (gypsum and halite minerals) along the outcrops of the high Atlas mountains. The data generated in this study provide the framework for a comprehensive management plan in which water exploitation should shift toward the eastern part of the basin where current recharge occurs with young and high quality groundwater. In contrast, we argued that the heavily exploited aquifer along the coastal areas is more vulnerable given the relatively longer residence time of the water and salinization processes in this part of the aquifer. ?? 2008 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2014

A data reconnaissance on the effect of suspended-sediment concentrations on dissolved-solids concentrations in rivers and tributaries in the Upper Colorado River Basin

The Colorado River is one of the most important sources of water in the western United States, supplying water to over 35 million people in the U.S. and 3 million people in Mexico. High dissolved-solids loading to the River and tributaries are derived primarily from geologic material deposited in inland seas in the mid-to-late Cretaceous Period, but this loading may be increased by human activities. High dissolved solids in the River causes substantial damages to users, primarily in reduced agricultural crop yields and corrosion. The Colorado River Basin Salinity Control Program was created to manage dissolved-solids loading to the River and has focused primarily on reducing irrigation-related loading from agricultural areas. This work presents a reconnaissance of existing data from sites in the Upper Colorado River Basin (UCRB) in order to highlight areas where suspended-sediment control measures may be useful in reducing dissolved-solids concentrations. Multiple linear regression was used on data from 164 sites in the UCRB to develop dissolved-solids models that include combinations of explanatory variables of suspended sediment, flow, and time. Results from the partial t -test, overall likelihood ratio, and partial likelihood ratio on the models were used to group the sites into categories of strong, moderate, weak, and no-evidence of a relation between suspended-sediment and dissolved-solids concentrations. Results show 68 sites have strong or moderate evidence of a relation, with drainage areas for many of these sites composed of a large percentage of clastic sedimentary rocks. These results could assist water managers in the region in directing field-scale evaluation of suspended-sediment control measures to reduce UCRB dissolved-solids loading.

Arizona, Colorado, New Mexico, Utah, Wyoming↗

USGS2020

Low streamflow trends at human-impacted and reference basins in the United States

We present a continent-scale exploration of trends in annual 7-day low streamflows at 2482 U.S. Geological Survey streamgages across the conterminous United States over the past 100, 75, and 50 years (1916–2015, 1941–2015 and 1966–2015). We used basin characteristics to identify subsets of study basins representative of reference basins with streamflow relatively free from human effects (n = 259), and predominantly agricultural basins (n = 78), regulated basins (n = 220), and urban basins (n = 121). Trend significance was computed using the Mann-Kendall test considering short- and long-term persistence. Lag-one autocorrelation tests of detrended 7-day low streamflows for all gage classes show that time-series independence is not an appropriate assumption for annual low streamflow data at many basins. Among all study gages, upward trends (wetter conditions) in 7-day low streamflows outnumbered downward trends (drier conditions) approximately 2–1 for the 75- and 100-year trend periods—50-year trends indicated roughly equal numbers of increases and decreases. Increases in 7-day low streamflow were consistently observed for all time periods throughout much of the northeastern quadrant of the conterminous U.S. including western New England and the Mid-Atlantic, the southeastern Great Lakes basin, northern Ohio River basin, and the Upper Mississippi River and eastern Missouri River basins. Decreases in 7-day low streamflow were consistently observed for all time periods at many gages in the southeastern U.S. and in the northwestern U.S. in much of Idaho and northwestern Washington. Overall, we observed greater percentages of statistically significant trends at gages with human-induced influences than at reference gages. Low-flow trends at agricultural gages were regionally consistent with trends at reference gages. Regulated basins had many statistically significant upward trends for all three time periods tested, which may be attributed in part to substantial increases in dam-related storage prior to 1970. Urban gages had the greatest percentage of significant decreases in 7-day low flows compared to all other gage classes even though most urban gages saw upward trends in mean annual flows. Urban gages also had the greatest percentage of significant increases in low flows second only to regulated gages, highlighting that urban development can increase or decrease low streamflows depending on the basin-specific development.

Conterminous United States↗

USGS2012

Predicting biological condition in southern California streams

As understanding of the complex relations among environmental stressors and biological responses improves, a logical next step is predictive modeling of biological condition at unsampled sites. We developed a boosted regression tree (BRT) model of biological condition, as measured by a benthic macroinvertebrate index of biotic integrity (BIBI), for streams in urbanized Southern Coastal California. We also developed a multiple linear regression (MLR) model as a benchmark for comparison with the BRT model. The BRT model explained 66% of the variance in B-IBI, identifying watershed population density and combined percentage agricultural and urban land cover in the riparian buffer as the most important predictors of B-IBI, but with watershed mean precipitation and watershed density of manmade channels also important. The MLR model explained 48% of the variance in B-IBI and included watershed population density and combined percentage agricultural and urban land cover in the riparian buffer. For a verification data set, the BRT model correctly classified 75% of impaired sites (B-IBI < 40) and 78% of unimpaired sites (B-IBI = 40). For the same verification data set, the MLR model correctly classified 69% of impaired sites and 87% of unimpaired sites. The BRT model should not be used to predict B-IBI for specific sites; however, the model can be useful for general applications such as identifying and prioritizing regions for monitoring, remediation or preservation, stratifying new bioassessments according to anticipated biological condition, or assessing the potential for change in stream biological condition based on anticipated changes in population density and development in stream buffers.

California↗

USGS2013

Environmental fate of fungicides and other current-use pesticides in a central California estuary

The current study documents the fate of current-use pesticides in an agriculturally-dominated central California coastal estuary by focusing on the occurrence in water, sediment and tissue of resident aquatic organisms. Three fungicides (azoxystrobin, boscalid, and pyraclostrobin), one herbicide (propyzamide) and two organophosphate insecticides (chlorpyrifos and diazinon) were detected frequently. Dissolved pesticide concentrations in the estuary corresponded to the timing of application while bed sediment pesticide concentrations correlated with the distance from potential sources. Fungicides and insecticides were detected frequently in fish and invertebrates collected near the mouth of the estuary and the contaminant profiles differed from the sediment and water collected. This is the first study to document the occurrence of many current-use pesticides, including fungicides, in tissue. Limited information is available on the uptake, accumulation and effects of current-use pesticides on non-target organisms. Additional data are needed to understand the impacts of pesticides, especially in small agriculturally-dominated estuaries.

California↗

USGS2015

A 3400 year paleolimnological record of prehispanic human–environment interactions in the Holmul region of the southern Maya lowlands

The timing, magnitude and drivers of late Holocene environmental change in the Holmul region of the southern Maya lowlands are examined by combining paleoenvironmental and archeological data. Environmental proxy analyses on a ~ 3350 cal yr lacustrine sediment record include pollen, charcoal, loss on ignition, magnetic suscep- tibility, and elemental geochemistry. Archeological evidence is derived from extensive settlement surveys conducted near the study site. Results indicate nearby settlement and agricultural activity taking place in an environment characterized by open forest from around 3350 to 950 cal yr BP. The fire history shows a dramatic increase in burning during the Classic period, possibly reflecting changing agricultural strategies. A distinct band of carbonate deposited from 1270 to 1040 cal yr BP suggests decreased hydrologic input associated with drier conditions. Abrupt changes in proxy data around 940 cal yr BP indicate a cessation of human disturbance and local abandonment of the area.

Peten↗

USGS2026

Millennial-scale climatic and cultural impacts on vegetation and fire at the southern edge of the Rocky Mountains, USA

Mountain forests and woodlands in semiarid regions of the world are threatened by climatic change and other human impacts. In the southwestern USA, climate and culturally driven changes to the structure and fire regimes of dry coniferous forests over recent centuries are well documented by tree-ring archives. However, the roles of climate and people as drivers of millennial-scale changes are less understood. We present a new record of vegetation dynamics and regional fire activity inferred from pollen, microscopic charcoal, and sediment geochemistry from Santa Fe Lake, NM (3532 m a.s.l.), the southernmost natural lake in the Rocky Mountains. Declining elemental intensities (e.g., Ti, Fe, Si) record local deglaciation after 14,000 cal yr BP followed by upslope expansion of trees indicated by increasing Pinus and Picea pollen percentages as the climate warmed during the Late Glacial. Cool, dry growing seasons probably limited the establishment of dense forests until after 12,200 cal yr BP when we hypothesize that Pinus ponderosa (ponderosa pine) expanded regionally (i.e., within 10–100 km) due to continued warming and a possible increase in monsoonal precipitation. Subalpine forests established near Santa Fe Lake by 10,300 cal yr BP as indicated by abundant conifer stomates and increasing Picea and Pinus aristata pollen percentages, which are highest after 5100 cal yr BP. Increasing Juniperus -type, Quercus , and Pinus edulis -type pollen record changes in vegetation belts at lower elevations after 10,300 cal yr BP. Maize pollen, an unambiguous indicator of Puebloan agriculture, first appears at 800 cal yr BP (1150 cal yr CE) and is present through 1600 cal yr CE when Spanish colonization brought cultural upheaval and population loss to local indigenous communities. Regional fire activity, inferred from microscopic charcoal influx, remained relatively constant for most of our record. However, average microscopic charcoal influx more than doubled relative to the rest of the Holocene during the last 2000 years, with the highest influx after 1550 cal yr BP (400 cal yr CE). The increased influx of microscopic charcoal coincides with archaeological evidence for dramatic regional population growth in the northern Rio Grande region and probably reflects extensive cultural burning associated with the development of an agricultural economy. Although climate was an important driver of vegetation change and fire regimes in the mountains of the southwestern USA during the Holocene, our results suggest that human impacts on regional burning during the last 2000 years far exceeded earlier climate-driven variation.

Rocky Mountains↗

USGS2009

Synthesis of ground and remote sensing data for monitoring ecosystem functions in the Colorado River Delta, Mexico

The delta of the Colorado River in Mexico supports a rich mix of estuarine, wetland and riparian ecosystems that provide habitat for over 350 species of birds as well as fish, marine mammals, and other wildlife. An important part of the delta ecosystem is the riparian corridor, which is supported by agricultural return flows and waste spills of water originating in the U.S. and Mexico. These flows may be curtailed in the future due to climate change and changing land use practices (out-of-basin water transfers, increased agricultural efficiency, and more optimal management of dams) in the U.S. and Mexico, and resource managers need to monitor the effects of their water management practices on these ecosystems. We developed ground-validated, remote sensing methods to monitor the vegetation status, habitat value, and water use of wetland and riparian ecosystems using multi-temporal, multi-resolution images. The integrated methodology allowed us to project species composition, leaf area index, fractional cover, habitat value, and evapotranspiration over seasons and years throughout the delta, in response to variable water flows from the U.S. to Mexico. Waste spills of water from the U.S. have regenerated native cottonwood and willow trees in the riparian corridor and created backwater and marsh areas that support birds and other wildlife. However, the main source of water supporting the riparian vegetation is the regional aquifer recharged by underflow from U.S. and Mexico irrigation districts. Native trees have a short half-life in the riparian zone due to human-set fires and harvesting for timber. Active management, monitoring, and restoration programs are needed to maintain the habitat value of this ecosystem for the future.

Colorado River Delta↗

USGS2013

Hyperspectral versus multispectral crop-productivity modeling and type discrimination for the HyspIRI mission

Precise monitoring of agricultural crop biomass and yield quantities is critical for crop production management and prediction. The goal of this study was to compare hyperspectral narrowband (HNB) versus multispectral broadband (MBB) reflectance data in studying irrigated cropland characteristics of five leading world crops (cotton, wheat, maize, rice, and alfalfa) with the objectives of: 1. Modeling crop productivity, and 2. Discriminating crop types. HNB data were obtained from Hyperion hyperspectral imager and field ASD spectroradiometer, and MBB data were obtained from five broadband sensors: Landsat-7 Enhanced Thematic Mapper Plus (ETM +), Advanced Land Imager (ALI), Indian Remote Sensing (IRS), IKONOS, and QuickBird. A large collection of field spectral and biophysical variables were gathered for the 5 crops in Central Asia throughout the growing seasons of 2006 and 2007. Overall, the HNB and hyperspectral vegetation index (HVI) crop biophysical models explained about 25% greater variability when compared with corresponding MBB models. Typically, 3 to 7 HNBs, in multiple linear regression models of a given crop variable, explained more than 93% of variability in crop models. The evaluation of λ 1 (400–2500 nm) versus λ 2 (400–2500 nm) plots of various crop biophysical variables showed that the best two-band normalized difference HVIs involved HNBs centered at: (i) 742 nm and 1175 nm (HVI742-1175), (ii) 1296 nm and 1054 nm (HVI1296-1054), (iii) 1225 nm and 697 nm (HVI1225-697), and (iv) 702 nm and 1104 nm (HVI702-1104). Among the most frequently occurring HNBs in various crop biophysical models, 74% were located in the 1051–2331 nm spectral range, followed by 10% in the moisture sensitive 970 nm, 6% in the red and red-edge (630–752 nm), and the remaining 10% distributed between blue (400–500 nm), green (501–600 nm), and NIR (760–900 nm). Discriminant models, used for discriminating 3 or 4 or 5 crop types, showed significantly higher accuracies when using HNBs (> 90%) over MBBs data (varied between 45 and 84%). Finally, the study highlighted 29 HNBs of Hyperion that are optimal in the study of agricultural crops and potentially significant to the upcoming NASA HyspIRI mission. Determining optimal and redundant bands for a given application will help overcoming the Hughes' phenomenon (or curse of high dimensionality of data).

Syr Darya River Basin↗