Assessment of downscaled current and future projections of diurnal rainfall patterns for the Himalaya

In this study we investigate the diurnal precipitation cycle in high-resolution regional climate simulations for present (2000-2010) and future time periods (2030-2040 and 2040-2050) over sub-regions of the Himalayas. The future periods are simulated under a high emission scenario, Representative Concentration Pathway 8.5 (RCP8.5) in order to maximize any projected externally driven precipitation signal. For present climate, 4-hourly simulated precipitation is first evaluated against observations to establish model credibility. The diurnal cycle, which is typically characterized by a bimodal structure with primary (secondary) maxima in nighttime (afternoon), is reasonably well represented in the present, giving us confidence when assessing potential future changes. The timing of the precipitation maxima and minima is found to match the observed timings well in the diurnal cycle. In general, the WRF model captures the principal shape of the diurnal cycle observed over all the sub-regions. Under projected future conditions, no significant changes in the diurnal cycle occur. The results suggest modest changes in diurnal precipitation under RCP8.5 emission scenario, as evidenced by an increase in afternoon precipitation around of the Himalayas. Although the projected future changes of precipitation presented in this article are within of the expected range of precipitation changes caution must be exercised when interpreting single-model experiments.