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