An evaluation of high-resolution gridded precipitation products over Bhutan (1998-2012)

Several global and regional high-resolution precipitation products have been released over the past decade by combining precipitation estimates from various sources including satellite-based measurements and gauge-based observations. With relatively few validation studies over the Eastern Himalayan region, this study examined seasonal and interannual skills of four gridded precipitation products including the regional gauge-based APHRODITE (Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of Water Resources) and three near-global satellite-based products: Tropical Rainfall Measuring Mission (TRMM), Climate Prediction Centre (CPC) MORPHing (CMORPH), and Climate Hazards Group InfraRed Precipitation (CHIRP) using in-situ rain gauge data from Bhutan for the period 1998-2012. Principal component analysis (PCA) was used to assess the dominant rainfall patterns over Bhutan. An attempt has also been made to correct precipitation biases in the satellite-only products using a gamma ()-based distribution approach. Results indicated that APHRODITE and satellite-based precipitation products were able to adequately capture the spatio-temporal patterns of rainfall variability over Bhutan. Extreme precipitation events and extreme drought periods were well captured with very good correlations (>0.5). APHRODITE and TRMM 3B43v7 were remarkably similar, whereas satellite-only products (CMORPH and CHIRP) highly underestimated (20-60% or 200-450 mm month(-1)) monsoon rainfall over Bhutan. While TRMM 3B43v7 still underestimated monsoon rainfall (by approximate to 25%), it has significantly improved the seasonal bias (by 20-40%) from its previous version (TRMM 3B43v6). CHIRP performed relatively better in the high rainfall regions but indicated very low correlations over mountainous regions and during the pre- and post-monsoon season. The bias correction approach indicated best results for TRMM 3B43v6 (up to 33%) in the Southern Foothills, whereas satellite-only products improved only moderately (5-20%).