*Article* **Evaluation of Evapotranspiration for Exorheic Catchments of China during the GRACE Era: From a Water Balance Perspective**

#### **Yulong Zhong 1,2,3, Min Zhong 3,4, Yuna Mao 5 and Bing Ji 6,\***


Received: 18 December 2019; Accepted: 4 February 2020; Published: 5 February 2020

**Abstract:** Evapotranspiration (ET) is usually di fficult to estimate at the regional scale due to scarce direct measurements. This study uses the water balance equation to calculate the regional ET with observations of precipitation, runo ff, and terrestrial water storage changes (TWSC) in nine exorheic catchments of China. We compared the regional ET estimates from a water balance perspective with and without considering TWSC (ETWB: ET estimates with considering TWSC, and ETPQ: ET estimates from precipitation minus runo ff without considering TWSC). Results show that the regional annual ET ranges from 417.7 mm/yr to 831.5 mm/yr in the nine exorheic catchments based on the water balance equation. The impact of ignoring TWSC on calculating ET is notable, as the root mean square errors (RMSEs) of annual ET between ETWB and ETPQ range from 12.0–105.8 mm/yr (2.6–12.7% in corresponding annual ET) among the exorheic catchments. We also compared the estimated regional ET with other ET products. Di fferent precipitation products are assessed to explain the inconsistency between di fferent ET products and regional ET from a water balance perspective. The RMSEs between ET estimates from Gravity Recovery and Climate Experiment (GRACE) and ET from land surface models can be reduced if the deviation of precipitation forcing data is considered. ET estimates from Global Land Evaporation Amsterdam Model (GLEAM) can be improved by reducing the uncertainty of precipitation forcing data in three semiarid catchments. This study emphasizes the importance of considering TWSC when calculating the regional ET using a water balance equation and provides more accurate ET estimates to help improve modeled ET results.

**Keywords:** evapotranspiration; China; exorheic catchments; water balance; GRACE; terrestrial water storage changes
