Approach for Estimating Available Consumable Water for Human Activities in a River Basin

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Evapotranspiration (ET) involves actual water consumption directly from the land surface; however, regional ET maps are usually neglected during water management and allocation. In this study, an integrated satellite-based ET monitoring approach with two spatial resolutions is proposed over an extremely arid basin in China that has experienced crop area expansion and has been the focus of a water-saving project since 2012. The proposed ETWatch approach combined with an empirical downscaling strategy based on vegetation condition was employed to produce monthly ET maps. This method achieves satisfactory accuracy and is validated by its reasonable spatial and temporal pattern results. Yearly results exhibit an increasing ET trend before 2012, which subsequently gradually decrease. This trend fits well with the dynamics of the basin-wide vegetation condition, indicating that there is a stronger correlation between water consumption and vegetation than between other environmental indicators. The average ET over three main crop types in the region (grape, cotton, and melon) decreased by approximately 5% due to optimizations of the irrigation timeline during the project, while 13% of the water savings can be attributed to the fallowing of crop areas. Based on the irrigation distribution in 2012, a comparison between drip and border irrigation that achieves water savings of 3.6% from grape and 5.8% from cotton is conducted. However, an afforestation project that involved planting young trees led to an approximate 25% increase in water consumption. Overall, since 2012, the water-saving project has achieved satisfactory performance regarding excessive groundwater withdrawal, showing a reduction trend of 3 million m3/year and an increase in Lake Aiding water levels since 2011. The results reveal the potential of the ET monitoring strategy as a basis for basin-scale water management.

Section: Discussionmentioning

confidence: 99%

Satellite-Based Water Consumption Dynamics Monitoring in an Extremely Arid Area

Tan

Niu

et al. 2018

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“…We chose the ETWatch model as the moderate-resolution ET data, as ETWatch is reliable for daily and monthly ET estimations across different climate types and surface characteristics, especially in cropland regions. Its accuracy has been proven by more than 50 research groups for water consumption structure and agricultural irrigation management, including our research region, Haihe Basin and Heihe Basin [7,8,14,16,30]. For ET calculations at high resolution, ETWatch has also been used as input data in several researches, including some downscaling methods [19,21].…”

Section: Introductionmentioning

confidence: 99%

“…These RS-based ET products provide regional and global ET results at daily or eight-day intervals with moderate spatial resolutions, usually at 500-m to one-km scales. Such ET data have been adopted for studying regional ecological impacts on water resources [14][15][16], modeling land-surface processes [17], analyzing water cycling, and evaluating regional available water resources [16]. However, the spatial scales of these moderate-resolution ET products are too coarse for agricultural water management, especially within small irrigation districts that usually occupy tens to hundreds of square meters, and detailed spatial information is omitted from km-level ET data.…”

Section: Introductionmentioning

confidence: 99%

Spatial Allocation Method from Coarse Evapotranspiration Data to Agricultural Fields by Quantifying Variations in Crop Cover and Soil Moisture

Niu

et al. 2021

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Cropland evapotranspiration (ET) is the major source of water consumption in agricultural systems. The precise management of agricultural ET helps optimize water resource usage in arid and semiarid regions and requires field-scale ET data support. Due to the combined limitations of satellite sensors and ET mechanisms, the current high-resolution ET models need further refinement to meet the demands of field-scale ET management. In this research, we proposed a new field-scale ET estimation method by developing an allocation factor to quantify field-level ET variations and allocate coarse ET to the field scale. By regarding the agricultural field as the object of the ET parcel, the allocation factor is calculated with combined high-resolution remote sensing indexes indicating the field-level ET variations under different crop growth and land-surface water conditions. The allocation ET results are validated at two ground observation stations and show improved accuracy compared with that of the original coarse data. This allocated ET model provides reasonable spatial results of field-level ET and is adequate for precise agricultural ET management. This allocation method provides new insight into calculating field-level ET from coarse ET datasets and meets the demands of wide application for controlling regional water consumption, supporting the ET management theory in addressing the impacts of water scarcity on social and economic developments.

“…Therefore, ET is a critical component of terrestrial ecosystems and profoundly impacts the water balance and energy cycle of the terrestrial surface [7,8]. Accurate ET estimates are vital to study hydrological processes from basin to regional levels [9][10][11][12][13], global climate change [14][15][16][17], drought and flood monitoring [18][19][20], water resource and optimal allocation management [21][22][23][24], agricultural water management and irrigation scheduling [25][26][27][28], environmental protection and ecological restoration [29,30]. Northern China has a complicated terrain and a large east-west span and is the country's main wheat and corn production area [31].…”

Section: Introductionmentioning

confidence: 99%

Synthesizing a Regional Territorial Evapotranspiration Dataset for Northern China

Wang

Elnashar

et al. 2021

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As a vital role in the processes of the energy balance and hydrological cycles, actual evapotranspiration (ET) is relevant to many agricultural, ecological and water resource management studies. The available global or regional ET products provide ET estimations with various temporal ranges, spatial resolutions and calculation methods (algorithms, inputs and parameterization, etc.), leading to varying degrees of introduced uncertainty. Northern China is the main agriculturally productive region supporting the whole country; thus, understanding the spatial and temporal changes in ET is essential to ensure water resource and food security. We developed a synthesis ET dataset for Northern China at a 1000 m spatial resolution, with a monthly temporal resolution covering a period ranging from 1982 to 2017, using an in-depth assessment of several ET products. Specifically, assessments were performed using in situ measured ET from eddy covariance (EC) observation towers at the site-pixel scale over interannual months under the conditions of different land cover types, climatic zones and elevation levels to select the most optimally performing ET products to be used in the synthesized ET dataset. Eight indicators under 21 conditions were involved in the assessment sheet, while the statistics of the different ET product occurrences and corresponding ratios were analyzed to select the best-performing ET products to build the synthesis ET dataset using the weighted mean method. The weights were determined by the Taylor skill score (TSS), calculated with ET products and EC ET observation data. Based on the assessment results, the Penman–Monteith–Leuning (PML_v2), ETWatch and Operational Simplified Surface Energy Balance (SSEBop) datasets were selected for implementation in the synthesis ET dataset from 2003 to 2017, while Global Land Evaporation Amsterdam Model (GLEAM) v3.3a, complementary relationship (CR) ET, and Numerical Terradynamic Simulation Group (NTSG) datasets were chosen for the synthesis ET dataset from 1982 to 2002. The weighted mean synthesized results from 2003 to 2017 performed well when compared to the in situ measured EC ET values produced under all of the above conditions, while the synthesized results from 1982 to 2002 performed well through the water balance method in Heihe River Basin. These results can provide more stable ET estimations for Northern China, which can contribute to relevant agricultural, ecological and hydrological studies.