Mapping evapotranspiration variability over a complex oasis-desert ecosystem based on automated calibration of Landsat 7 ETM+ data in SEBAL

Fragmented ecosystems of the desiccated Aral Sea seek answers to the profound local hydrologically- and water-related problems. Particularly, in the Small Aral Sea Basin (SASB), these problems are associated with low precipitation, increased temperature, land use and evapotranspiration (ET) changes. Here, the utility of high-resolution satellite dataset is employed to model the growing season dynamic of near-surface fluxes controlled by the advective effects of desert and oasis ecosystems in the SASB. This study adapted and applied the sensible heat flux calibration mechanism of Surface Energy Balance Algorithm for Land (SEBAL) to 16 clear-sky Landsat 7 ETM+ dataset, following a guided automatic pixels search from surface temperature T-s and Normalized Difference Vegetation Index NDVI (). Results were comprehensively validated with flux components and actual ET (ETa) outputs of Eddy Covariance (EC) and Meteorological Station (KZL) observations located in the desert and oasis, respectively. Compared with the original SEBAL, a noteworthy enhancement of flux estimations was achieved as follows: - desert ecosystem ETa R-2 = 0.94; oasis ecosystem ETa R-2 = 0.98 (P < 0.05). The improvement uncovered the exact land use contributions to ETa variability, with average estimates ranging from 1.24 mm to 6.98 mm . Additionally, instantaneous ET to NDVI (ETins-NDVI) ratio indicated that desert and oasis consumptive water use vary significantly with time of the season. This study indicates the possibility of continuous daily ET monitoring with considerable implications for improving water resources decision support over complex data-scarce drylands

Assessing Spatiotemporal Drought Dynamics and Its Related Environmental Issues in the Mekong River Delta

Drought is a major natural disaster that creates a negative impact on socio-economic development and environment. Drought indices are typically applied to characterize drought events in a meaningful way. This study aims at examining variations in agricultural drought severity based on the relationship between standardized ratio of actual and potential evapotranspiration (ET and PET), enhanced vegetation index (EVI), and land surface temperature (LST) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) platform. A new drought index, called the enhanced drought severity index (EDSI), was developed by applying spatiotemporal regression methods and time-series biophysical data derived from remote sensing. In addition, time-series trend analysis in the 2001–2018 period, along with the Mann–Kendal (MK) significance test and the Theil Sen (TS) slope, were used to examine the spatiotemporal dynamics of environmental parameters (i.e., LST, EVI, ET, and PET), and geographically weighted regression (GWR) was subsequently applied in order to analyze the local correlations among them. Results showed that a significant correlation was discovered among LST, EVI, ET, and PET, as well as their standardized ratios (|r| > 0.8, p 0.7 and a statistical significance p < 0.01. Besides, it was found that the temporal tendency of this phenomenon was the increase in intensity of drought, and that coastal areas in the study area were more vulnerable to this phenomenon. This study demonstrates the effectiveness of EDSI and the potential application of integrating spatial regression and time-series data for assessing regional drought conditions

The interacting hydrologic responses to changing climate, watershed physical characteristics, river regulation, and land development in the northeastern United States

In this dissertation, the scale-dependency of hydrologic responses due to changing climate and regime shifts of large-scale circulation patterns and their teleconnection patterns were evaluated using long-term precipitation and discharge records in sub-basins with no development, and extensive development and riverine impoundments of the Merrimack River watershed. The Merrimack (New Hampshire-Massachusetts) is a 13,000 km2 forested (67%) watershed located in the northeastern United States. The overarching goal of this dissertation was to assess hydrologic responses to the potential effects of changing climate in sub-basins experiencing a range of development in order to help guide sustainable water management in the Merrimack River watershed and other northeastern basins. The objective of this research was to integrate hydroclimatic observations across basin size and anthropogenic disturbances (i.e. river regulation and land development) to understand the dynamic of hydrologic alterations under a changing climate. This dissertation consists of three research phases. In phase I, I assessed the interacting hydrologic responses to changing climate, watershed physical characteristics, river regulation, and land development under dry, average, and wet hydrologic conditions using long-term precipitation and discharge data of the Merrimack River watershed. I found that the effects of basin scale were limited to high (exceedance probability of less than 15%) and low (exceedance probability of greater than 60%) discharge events and were expressed as lagged discharge in larger sub-basins and earlier discharge in smaller headwater catchments. Annual discharge responded to increases in annual precipitation regardless of river regulation or land development. In general, the temporal trends showed greater decreasing trends in discharge under dry and greater increasing trends in discharge under wet hydrologic conditions compared to average years. In phase II, I explored the effects of Atlantic Multi-decadal Oscillation (AMO: metric of Sea Surface Temperature anomalies of the North Atlantic Ocean typically over 0-80°N) and North Atlantic Oscillation (NAO: metric of Sea-Level Pressure anomalies over the Atlantic sector 20°-80°N, 90°W-40°E) regime shifts on hydrologic responses to evaluate whether the intensified inter-annual variability in discharge is explained by natural climate cycles. I focused on AMO and NAO regime shifts of the early 1950s, 1970s, and 2000s and the effects on hydrology of the Merrimack River watershed. AMO regime shifts were strongly synchronized and preceded both precipitation and discharge across all study sites by one to two years, while NAO regime shifts indicated weaker associations. I found that all responses tended towards greater extremes from each regime shift to the next. Across many different ecological discharge indicators, high percentile values increased across regimes, while low percentile values decreased between regimes (with a few exceptions). In phase III, I evaluated the potential for discharge estimation considering annual or seasonal AMO and NAO teleconnection patterns with precipitation and discharge. When AMO was extremely positive (greater than 0.2), the magnitudes of annual precipitation and discharge correlation coefficients with AMO were obscured by river regulation or land development. In contrast, during the extreme negative phase of AMO (less than 0.2), river regulation and land development amplified the effects of changing climate on precipitation and discharge variations. AMO was positively associated with precipitation and discharge, while NAO showed a negative linkage. AMO positive phase was correspondent with average-to-wet discharge conditions at headwater catchments. When basin scale increased, confidence in the estimation of discharge conditions decreased for downstream developed sub-basins compared to headwater undisturbed catchments. The results from this research indicated that the Merrimack River watershed is expected to experience increases in discharge in the future and changing in timing and the seasonal distribution of this discharge; therefore development should be avoided on flood plains. Furthermore, the current reservoir storage capacity in the Merrimack should be improved in order to accommodate excess water input and minimize flood damage. Future research should target changes in the magnitude and timing of high discharge events in order to develop adaptation strategies for aging hydraulic infrastructure in the region. This dissertation will provide information for watershed planners and managers to inform future sustainable water use in the Merrimack River watershed and other northeastern basins

Earth observation-based operational estimation of soil moisture and evapotranspiration for agricultural crops in support of sustainable water management

Global information on the spatio-temporal variation of parameters driving the Earth’s terrestrial water and energy cycles, such as evapotranspiration (ET) rates and surface soil moisture (SSM), is of key significance. The water and energy cycles underpin global food and water security and need to be fully understood as the climate changes. In the last few decades, Earth Observation (EO) technology has played an increasingly important role in determining both ET and SSM. This paper reviews the state of the art in the use specifically of operational EO of both ET and SSM estimates. We discuss the key technical and operational considerations to derive accurate estimates of those parameters from space. The review suggests significant progress has been made in the recent years in retrieving ET and SSM operationally; yet, further work is required to optimize parameter accuracy and to improve the operational capability of services developed using EO data. Emerging applications on which ET/SSM operational products may be included in the context specifically in relation to agriculture are also highlighted; the operational use of those operational products in such applications remains to be seen

Water Resource Variability and Climate Change

Climate change affects global and regional water cycling, as well as surficial and subsurface water availability. These changes have increased the vulnerabilities of ecosystems and of human society. Understanding how climate change has affected water resource variability in the past and how climate change is leading to rapid changes in contemporary systems is of critical importance for sustainable development in different parts of the world. This Special Issue focuses on “Water Resource Variability and Climate Change” and aims to present a collection of articles addressing various aspects of water resource variability as well as how such variabilities are affected by changing climates. Potential topics include the reconstruction of historic moisture fluctuations, based on various proxies (such as tree rings, sediment cores, and landform features), the empirical monitoring of water variability based on field survey and remote sensing techniques, and the projection of future water cycling using numerical model simulations

Spatiotemporal Variations of Reference Crop Evapotranspiration in Northern Xinjiang, China

To set up a reasonable crop irrigation system in the context of global climate change in Northern Xinjiang, China, reference crop evapotranspiration (ET 0 ) was analyzed by means of spatiotemporal variations. The ET 0 values from 1962 to 2010 were calculated by Penman-Monteith formula, based on meteorological data of 22 meteorological observation stations in the study area. The spatiotemporal variations of ET 0 were analyzed by Mann-Kendall test, Morlet wavelet analysis, and ArcGIS spatial analysis. The results showed that regional average ET 0 had a decreasing trend and there was an abrupt change around 1983. The trend of regional average ET 0 had a primary period about 28 years, in which there were five alternating stages (high-low-high-low-high). From the standpoint of spatial scale, ET 0 gradually increased from the northeast and southwest toward the middle; the southeast and west had slightly greater variation, with significant regional differences. From April to October, the ET 0 distribution significantly influenced the distribution characteristic of annual ET 0 . Among them sunshine hours and wind speed were two of principal climate factors affecting ET 0

IRRIGATION IN THE WESTERN UNITED STATES: OCCURRENCE, IMPACTS, AND SUSTAINABILITY

Irrigation represents our greatest intervention in the hydrological cycle, accounting for over 80% of extracted freshwater in the Western U.S. Despite its economic and ecological importance, irrigation’s spatial and temporal occurrence, magnitude, impacts on streamflow, and response during water shortages has not been characterized in our region. The major objective of this dissertation was to systematically assess irrigation over the Western US to answer the following questions: 1) Where and when does irrigation occur within the study region? 2) How has the intensity, area, and distribution of irrigation changed over the course of the past 35 years? 3) What impact is irrigation having on surface water (i.e., rivers) in the region, how do impacts differ across basins, and what is driving them? 4) Finally, how do irrigators respond to drought and what can be expected of the irrigated system during water scarce times? To answer these questions, we developed a 35-year dataset covering the western U.S. consisting of high resolution satellite-derived irrigation and evapotranspiration data alongside streamflow, field-scale agricultural boundaries, and detailed climate information. We used a combination of data-driven methods to infer the behavior of irrigation in time and space, Bayesian regression modeling to define relationships between climate, irrigation and streamflow, and detailed geospatial and economic data analysis to explore drivers of the behavior of irrigated systems. We show that both climate change and irrigation are impacting streamflows, and that contrary to government statistics, irrigation is expanding in intensity, area, and water use. We show evidence for the large-scale operation of the ‘paradox of irrigation efficiency’, where despite increasing on-farm irrigation efficiency enabled by advances in irrigation infrastructure, basin-scale crop water use increases. We show how streamflow is changing and where the changes are driven by changes in climate and irrigation. Finally, we show that crop prices appear to drive crop planting decisions (and thus irrigated water use) to a greater degree than seasonal climate conditions and that intensely irrigated regions are unresponsive to drought. This dissertation contributes to our understanding of the systems-level impact of irrigation and provides opportunities for basin-specific management actions to mitigate irrigation and climate impacts on streamflow

A Reconstruction of Irrigated Cropland Extent in China from 2000 to 2019 Using the Synergy of Statistics and Satellite-Based Datasets

Irrigated agriculture has undergone rapid developments in China, which has greatly increased food production but overexploited water resources as well. Spatial information on irrigated cropland is critical to balance irrigation yield gains against the negative impact on water resources. However, remote-sensing-based maps on irrigated areas with short temporal coverage often suffer from undermined accuracy in humid areas and inconsistency with statistics, which limit their applications in food policy and water management. The following study integrates existing irrigation maps, observed data on irrigated cropping system, and statistics by a synergy approach to map irrigated areas in China from 2000 to 2019. We also incorporate past information on actual irrigation to avoid divergence between observations and statistics from its fluctuation. Afterwards, 614 reference samples across mainland China have been used to validate resultant maps, which show that outperformance was above overall accuracy and Kappa coefficients. Moreover, our maps share a similar spatial pattern with Irrimap-Syn maps rather than remote-sensing-based maps (CCI-LC). Irrigated areas have grown rapidly from 55.42 Mha in 2000 to 71.33 Mha in 2019 but with different growth trends in different regions. Simultaneous large-scale expansion and abandonment occur in the Huang-Huai-Hai Plain and Yangtze River Basin, while the Northwest Inland Region and the Northeast Plain are the two largest net area gains. Rainfed croplands are dominant sources of expansion, followed by pastures, respectively, with over 70% and 20% contributions in total gains. This not only is a shift from rainfed to irrigated systems but also indicates an intensification of agriculture, which might contribute to agricultural drought reductions in the north and wide soil suitability. Other efforts on agricultural sustainability also have been detected, such as geographical shifts from vulnerable to relatively suitable areas, grain for green, cropland protection, and cropland protection in the competition of urbanization

Reconstructed springtime (March–June) precipitation tracked by tree rings dating back to 1760 CE in the Qinling-Bashan mountainous area

In recent decades, considerable advances have been made in dendroclimatic reconstruction in the eastern monsoon region of China. However, understanding of long-term hydroclimatic changes has not been comprehensive due to the complexity of the regional geography in China's north-south transitional zone. Growth-climate response analysis indicated that springtime precipitation is the main factor limiting the radial growth of pine trees in the Qinling-Bashan mountainous area. Based on the three tree ring chronologies distributed in the southeast of Shaanxi Province, we developed a March–June precipitation reconstruction spanning 1760–2020 CE for the Qinling-Bashan mountainous area. Precipitation reconstruction accounts for 40.6% of the total precipitation variance during the instrumental period 1955–2016. Spatial correlation analysis indicated that the precipitation reconstruction recorded similar common precipitation signals for the eastern Qinling Mountains and the Yangtze-Huai River Basin. The results of the superposed epoch analysis (SEA) revealed that low precipitation was one of the main causes of severe drought and locust plague events. The preliminary synoptic climatology analysis showed that our reconstructed precipitation is closely linked to the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) variability.Fil: Wang, Shijie. Yunnan University; ChinaFil: Man, Wenmin. Chinese Academy of Sciences; República de ChinaFil: Chen, Feng. Yunnan University; China. China Meteorological Administration; ChinaFil: Chen, Youping. Yunnan University; ChinaFil: Yu, Shulong. China Meteorological Administration; ChinaFil: Cao, Honghua. Yunnan University; ChinaFil: Hu, Mao. Yunnan University; ChinaFil: Hou, Tiyuan. Yunnan University; ChinaFil: Hadad, Martín Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Roig Junent, Fidel Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Mayor; Chil