Alp-valley and elevation effects on the reference evapotranspiration and the dominant climate controls in Red River Basin, China: Insights from geographical differentiation

[Display omitted] •Schematic diagram clarifies Alp-valley and elevation effects on ET0 and its drivers.•RRBC’s ET0 increases as elevation increases, declines from northwest to southeast.•Barrier-Corridor effect makes ET0 differ in Alp sides, increase along the valley.•RRBC is wet in the southwest, wet in the west side of Ailao, dry-hot in the valley.•Rs reduces dominant impact on ET0 with elevation increase as RH, T and U increase. Complicated topography can drastically affect the geographical distribution of evaporation, runoff production, water cycle, and water security guarantee. However, whether the elevation and Alp-valley have differentiated effects on basin evaporation and handle the change with constant variables is still being determined. This manuscript calculates reference evapotranspiration (ET0) of the Red River Basin with a typical Alp-valley and elevation gradient from 1960 to 2021. Then at the scales of the whole basin, both sides of the main Alp (western of Ailao mountain (WAL) and eastern of Ailao mountain (EAL)), the mainstream valley (Yuanjiang valley (YJV)), the spatial–temporal distribution pattern of ET0 and its sensitivity of climate variables are depicted from the insights of barrier-corridor and elevation effects. The results indicate that ET0 grows at a rate of 27.77 mm per decade throughout the Red River Basin, China (RRBC), gradually declines from northwest to southeast, and increases with increasing elevation. The barrier effect of the Ailao Mountains within the RRBC alters the elevation distribution pattern of ET0 on both sides of the mountain. In contrast, the corridor effect along the YJV causes the ET0 increases with the depth of the valley. Accordingly, the aridity index increases with rising elevation resulting in drier climatic conditions in the north of the RRBC, and suffers a significant influence from Alp-valley topography resulting in wet WAL, dry EAL and drier YJV. The topography plays an impact on ET0 through the climatic control variables. Solar radiation (Rs) has the highest impact on ET0, followed in descending order by relative humidity (RH), air temperature (T) and wind speed (U). With the elevation increases, Rs and T reduce the effect on ET0, whereas RH increases its effect. Also, the barrier effect changed the dominant factors: Rs and RH control the ET0 on WAL and EAL, respectively, while the corridor effect enhances the role of T and U. Moreover, the schematic diagram of the ET0’s change with elevation gr