PNNL

Abstract

The future state of the global water cycle and prediction of freshwater availability for 41 humans around the world remain among the challenges of climate research and are relevant to 42 several United Nations Sustainable Development Goals. The Global Precipitation EXperiment 43 (GPEX) takes on the challenge of improving the prediction of precipitation quantity, phase, 44 timing and intensity, characteristics that are products of a complex integrated system. It will 45 achieve this by leveraging existing World Climate Research Programme (WCRP) activities 46 and community capabilities in satellite, surface-based, and airborne observations, modeling 47 and experimental research, and by conducting new and focused activities. It was launched in 48 October 2023 as a WCRP Lighthouse Activity. Here we present an overview of the GPEX 49 Science Plan that articulates the primary science questions related to precipitation 50 measurements, process understanding, model performance and improvements, and plans for 51 capacity development. The central phase of GPEX is the WCRP Years of Precipitation for 2-3 52 years with coordinated global field campaigns focusing on different storm types (atmospheric 53 rivers, mesoscale convective systems, monsoons, and tropical cyclones, among others) over 54 different regions and seasons. Activities are planned over the three phases (before, during, and 55 after the Years of Precipitation) spanning a decade. These include gridded data evaluation and 56 development, advanced modeling, enhanced understanding of processes critical to 57 precipitation, multi-scale prediction of precipitation events across scales, and capacity 58 development. These activities will be further developed as part of the GPEX Implementation 59 Plan.