Estimating Actual Evapotranspiration over Croplands Using Vegetation Index Methods and Dynamic Harvested Area

Abstract

Advances in estimating actual evapotranspiration (ETa) with remote sensing (RS) have contributed to improving hydrological, agricultural, and climatological studies. In this study, we evaluated the applicability of Vegetation-Index (VI) -based ETa (ET-VI) for mapping and monitoring drought in arid agricultural systems in a region where a lack of ground data hampers ETa work. To map ETa (2000–2019), ET-VIs were translated and localized using Landsat-derived 3- and 2-band Enhanced Vegetation Indices (EVI and EVI2) over croplands in the Zayandehrud River Basin (ZRB) in Iran. Since EVI and EVI2 were optimized for the MODerate Imaging Spectroradiometer (MODIS), using these VIs with Landsat sensors required a cross-sensor transformation to allow for their use in the ET-VI algorithm. The before- and after- impact of applying these empirical translation methods on the ETa estimations was examined. We also compared the effect of cropping patterns’ interannual change on the annual ETa rate using the maximum Normalized Difference Vegetation Index (NDVI) time series. The performance of the different ET-VIs products was then evaluated. Our results show that ETa estimates agreed well with each other and are all suitable to monitor ETa in the ZRB. Compared to ETc values, ETa estimations from MODIS-based continuity corrected Landsat-EVI (EVI2) (EVIMccL and EVI2MccL) performed slightly better across croplands than those of Landsat-EVI (EVI2) without transformation. The analysis of harvested areas and ET-VIs anomalies revealed a decline in the extent of cultivated areas and a loss of corresponding water resources downstream. The findings show the importance of continuity correction across sensors when using empirical algorithms designed and optimized for specific sensors. Our comprehensive ETa estimation of agricultural water use at 30 m spatial resolution provides an inexpensive monitoring tool for cropping areas and their water consumption.

Seasonal variations of vegetative indices and their correlation with evapotranspiration and soil water storage in a small agricultural catchment

“…However, the relationship between VIs and ET is not always linear but rather depends on various factors such as net radiation, temperature, soil moisture, and vegetation characteristics (Wang et al 2007 2013) developed an exponential model using MODISbased EVI as a surrogate for LAI to estimate the actual evapotranspiration in riparian zones (Nagler et al 2005(Nagler et al , 2020. Abbasi et al (2021) further adapted this exponential model to investigate the ET-VIs correlations for croplands at 30 m resolution and found good agreement with ground measurements. These studies suggest that VIs can be useful indicators of ET dynamics in different ecosystems, but they require site-specific calibration and validation.…”

Crop production in Türkiye: trends and driving variables

“…However, performing large-scale assessments using point base observations is challenging. Remote sensing can provide a comprehensive overview for capturing the signal of such drivers on harvested area and yield at regional scale (Kern et al 2018, Joglekar et al 2019, Wolanin et al 2020, Abbasi et al 2021. It is unknown whether contribution of harvested area and yield fluctuations in crop production variability is crop specific and whether remote sensing is effective in monitoring these fluctuations in Türkiye.…”

Estimation of Actual Evapotranspiration (ETa) of Major Crops of a Distributary of Mahanadi Canal Command Using CROPWAT 8.0 Model by Penman: Montieth Method

“…To better estimate crop water requirements, Food and Agriculture Organization recommends the use of CROPWAT software, CROPWAT is frequently used for crop evapotranspiration, reference crop evapotranspiration, irrigation scheduling, and cropping patterns prediction. The study help on using CROPWAT model for estimating actual evapotranspiration [7][8][9][10][11].…”