Rainfall Estimation From The Bottom: The Power Of Soil Moisture

Rainfall is the main driver of the hydrological cycle. Its estimation is fundamental in many applications like climate monitoring, extreme weather prediction, and weather forecasting. Rainfall at the ground level is measured by instruments called rain gauges. However, the number of rain gauges is limited and unevenly distributed over the world.

Alternatively, we can use remote sensing that guarantees global coverage and repetitive measurements. Space agencies have been launching missions explicitly dedicated to rainfall measurement through a “top-down” approach, which provides instantaneous rainfall estimates based on the inversion of the atmospheric signals reflected or radiated by clouds. However, snapshot measurements might not be able to accurately estimate rainfall, due to its high intermittency.


An alternative and innovative approach, named SM2RAIN, has been developed 5 years ago by the Hydrology group of the Research Institute for Geo-Hydrological Protection of the National Research Council in Italy. SM2RAIN is able to estimate rainfall through measurements of soil moisture following a “bottom-up” approach. Since the first publication (Brocca et al., 2013), SM2RAIN has been continuously improved and employed in numerous analyses from local to global scale (Brocca et al., 2017).

Comparisons with the state-of-the-art “top-down” satellite rainfall products, demonstrated that SM2RAIN often results more accurate, especially in Southern Africa, Southern America, India, Australia, Western USA, and Southern Europe (Ciabatta et al., 2018; Massari et al., 2017). Also, the integration of the highly complementary “bottom-up and “top-down” approaches already provided very promising results (Chiaravallotti et al., 2018).

Global scale performance of the recent SM2RAIN-ASCAT rainfall product (1-day, 12.5 km resolution): Correlation (R) and Root Mean Square Error (RMSE) in a single map for the comparison with ERA5 ECMWF reanalysis in the period 2012-2017. Credit: Luca Brocca

A very recent application of SM2RAIN has been proposed in Tarpanelli et al. (2017) who exploited a constellation of satellite soil moisture sensors (Advanced SCATterometer, ASCAT; Advanced Microwave Scanning Radiometer 2, AMSR-2; Soil Moisture Active and Passive mission, SMAP; Soil Moisture and Ocean Salinity mission, SMOS, and RapidScat) for estimating rainfall.

The authors demonstrated that the joint use of multiple soil moisture sensors improves not only the temporal resolution but also the accuracy, thus providing a superior “bottom-up” rainfall product with performance comparable or better than the products derived from the new Global Precipitation Measurement (GPM) mission by NASA. Among the real-world applications, SM2RAIN-derived rainfall products are highly useful for improving floods and landslides prediction (Massari et al., 2018), for water budget modeling (Abera et al., 2016), and for climate and agricultural applications (Brocca et al., 2017).


Among the future applications, the use of high-resolution soil moisture product from the new ESA mission, Sentinel-1, will be an important extension of the analysis to obtain a rainfall product with 1-km spatial resolution. Luca Brocca, the author of the first paper on SM2RAIN says “It is now possible to obtain satellite soil moisture data at 100 m or even 10 m resolution, which of course changes the number of potential applications which could get benefit from them. For example, in Italy and in the Mediterranean area, we have the problem of flash floods. These types of floods evolve very quickly in small to medium catchments and are very difficult to predict. These new satellite products could help us with that. I am guessing these new high-resolution products will be available in the next 1 or 2 years.”

These findings are described in the article entitled Exploiting a constellation of satellite soil moisture sensors for accurate rainfall estimation, recently published in the journal Advances in Water Resources. This work was conducted by A. Tarpanelli, C. Massari, L. Ciabatta, L. Brocca, and P. Filippucci from the Research Institute for Geo-hydrological Protection, and G. Amarnath from the International Water Management Institute.



Political Map Of The World

Everyone knows what a map is. Maps, in general, are a pictorial representation of some place that allows people to […]

Antioxidant Carnosic Acid Found To Protect Human Mitochondria

Carnosic acid (CA, C20H28O4) is characterized as a phenolic diterpene and has been isolated from the Rosmarinus officinalis L. plant. This […]

Finding Time For Evolution

Time is a concept that is taken for granted in most areas of human life. It is treated casually without […]

Vulnerability Of Antarctic Marine Ecosystem Engineers With Skeletal Magnesium Content In A Changing World

The oceans are being impacted by climate change from rising atmospheric CO2 levels and increasing pollution (e.g. petroleum hydrocarbons and […]

Flagella: Function And Definition

Flagella are commonly found in bacteria, but can also be found in archaea and eukaryotic organisms as well. A flagellum […]

Cephalostatin 1 Analogues: Promising Anti-Tumor Drugs 

Cancer is a leading cause of death worldwide, and the number of deaths is projected to continuously rise in the […]

Studying The Orbit Lifetimes Of Spacecrafts Around Moons: The Callisto-Jupiter System Case

Space exploration has occupied a major impact on the changes that the modern society has experienced. The range of benefits […]

Science Trends is a popular source of science news and education around the world. We cover everything from solar power cell technology to climate change to cancer research. We help hundreds of thousands of people every month learn about the world we live in and the latest scientific breakthroughs. Want to know more?