Sensitivity of Evapotranspiration, Total Water Storage Change and Discharge to different Potential Evapotranspiration Methods

Hydrological models are effective tools for understanding and quantifying changes in wateravailability over time. These models excel in quantifying various hydrological components suchas runoff (Q), total water storage (TWS), evapotranspiration (ET) . Precipitation (P) and Po-tential Evapotranspiration (PET) are the most important required inputs for modeling thesecomponents. In modeling, sensitivity of P is well-acknowledged. However, a notable gap existsin assessing the sensitivity of PET methods in hydrological models. This study systematicallyexamines the sensitivity in terms of slopes, of 12 distinct PET methods spanning differentclasses (temperature-based, radiation-based and their combinations) on ET, total water stor-age change (TWSC) and Q. More than 100 European catchments were studied using mesoscaleHydrological Model (mHM). Our results show that PET methods differ significantly at annualand seasonal scales. For instance, overall annual PET ranges from approximately 250-2200mm/year across European catchments. PET increases from energy-limited to water-limitedcatchments. Temperature-based PET methods is higher in magnitude than radiation and com-binational type at summer, spring-season, and annual scale. No clear pattern was observed forthe winter and autumn season. We also examined ET, Q, and TWSC slopes and comparedthem with PET’s slopes. Our study illuminates the pivotal role of PET methods in hydrologicalmodeling, emphasizing the need for researchers to select PET methods judiciously accordingto the specific objectives of their studies.