The frequency of summer light rain projections in typical terrain over eastern China constrained by surface wind speed

Abstract

The variation of near surface wind speed is a key dynamic parameter in the orographic effect of precipitation over eastern China. In this study, we used the latest high-resolution outputs from six GCMs in CMIP6-HighResMIP to evaluate the performance of high-resolution models in simulating the orographic precipitation characteristics of typical mountainous areas in summer over eastern China. Combined with observational results, the orographic precipitation under warming scenarios was projected and constrained. The results indicated that during the contemporary climate reference period (1979-2009), although the relationship between model-simulated near surface wind speed and the orographic light rain frequency was consistently stable, the sensitivity of the orographic light rain frequency to surface wind variability was generally underestimated, with a deviation approximately 24.1% lower than the observational values. Comparison of model-simulated wind speed with observational records showed that the negative bias of the sensitivity value was mainly contributed by the overestimated wind speed in models. Based on observed near-surface wind speed to constrain and correct the orographic light rain frequency, the constrained estimates revealed a 36.1% reduction in orographic light rain frequency under a 1.5°C warming scenario, which is 8.6 times greater than the original predictions (4.2%). The MRI-AGCM3-2-S model, with a longer dataset, demonstrated a relatively stable reduction in orographic light rain frequency under different warming scenarios (1.5°C, 2°C, 3°C, and 4°C) after wind speed constraints, all of which are exceeding the original predictions.