Assessing the accuracy and drought utility of long-term satellite-based precipitation estimation products using the triple collocation approach

Satellite-based precipitation products (SPP) have been the focus of much attention for their potential utility of drought monitoring and analysis. Assessing the accuracy and drought performance of the SPPs for ungauged areas is urgent and also challenging. This study comprehensively investigated the performance of the triple collocation (TC) approach, an assessment approach requiring no benchmark data, the accuracy and drought utility assessment of the SPPs. Furthermore, we applied the TC approach experimentally to the SPPs throughout mainland China. The China monthly Precipitation Analysis Product (CPAP), a gridded gauge-based precipitation dataset, was employed to validate the TC approach. Results demonstrate the effectiveness of the TC approach in retrieving spatial patterns in the accuracy and drought performance (via short-timescale drought indices) of the SPPs, but systematic bias was observed. Moreover, the TC approach exhibits a weak performance in assessing the long-timescale drought indices. By comparing the assessment results, the TC approach reveals the potential underestimation of the SPP accuracy by the traditional assessment approach for some ungauged regions. In general, the proposed TC outperforms the traditional approach in qualitatively assessing the performance pattern of SPPs over ungauged and poorly gauged areas, but the systematic bias of TC needs attention when quantitatively determining SPP performance.