From SMOS Soil Moisture to 3-hour Precipitation Estimates at 0.1° Resolution in Africa

Thierry Pellarin,Yann H Kerr,Nathalie Philippon,Geremy Panthou,Jean-Martial Cohard,Carlos Román-Cascón,Nemesio Rodriguez-Fernandez,Alexandre Zoppis

doi:10.3390/rs14030746

Abstract

Several recent studies have shown that knowledge of the spatiotemporal dynamics of soil moisture intrinsically contains information on precipitation. In this study, we show how SMOS measurements can be used to generate a near-real-time precipitation product with a spatial resolution of 0.1° and a temporal resolution of 3 h. The principle consists of assimilating the SMOS data into a model that simulates the evolution of soil moisture, which is forced by a satellite precipitation product. The assimilation of SMOS soil moisture leads to an adjustment of the satellite precipitation rates. Using data from more than 200 rain gauges set up in Africa between 2010 and 2021, we show that the PrISM algorithm (for Precipitation Inferred from Soil Moisture) almost systematically improves the initial precipitation product. One of the original features of this study is that we used the IMERG-Early satellite precipitation product, which has a finer spatial resolution (0.1°) than SMOS (~0.25°). Despite this, the methodology reduces both the RMSE and bias of IMERG-Early. The RMSE is reduced from 8.0 to 6.3 mm/day, and the absolute bias is reduced from 0.81 to 0.63 mm/day on average over the 200 rain gauges. PrISM performs even slightly better on average than IMERG-Final in terms of RMSE (6.8 mm/day for IMERG-Final) but better scores are obtained by IMERG-Final in terms of absolute bias (0.35 mm/day), which utilizes a network of field measurements to correct the biases of the IMERG-Early product with a 2.5-month delay. Therefore, the use of SMOS soil moisture measurements for Africa can be an advantageous alternative to the use of gauge measurements for debiasing rainfall satellite products in real time.

Highlights

Introduction published maps and institutional affilPrecipitation is a vital resource in Africa, where a large proportion of the population depends on rain-fed agriculture
Africa is one of the most vulnerable regions in the world to climate change, which has an impact on natural resources and on the well-being of populations in societies where the economy is mainly based on agriculture [1]
Africa does not have a dense network of rain gauges and operational radar facilities are almost non-existent [2]

Summary

Introduction

Precipitation is a vital resource in Africa, where a large proportion of the population depends on rain-fed agriculture. Africa is one of the most vulnerable regions in the world to climate change, which has an impact on natural resources (water, vegetation) and on the well-being of populations in societies where the economy is mainly based on agriculture [1]. Knowledge of the spatiotemporal distribution of rainfall is essential for various applications such as water resources management, flood forecasting, dam management, agricultural crop yield estimates, groundwater recharge estimation and irrigation demand. Rain gauges provide the most common and direct measurement of precipitation at a point and are generally considered the most accurate method of measuring rainfall. The number of rain gauges is often below the minimum recommended by the World Meteorological Organization (WMO) and iations

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Conclusion