A case study of rainfall evaporation using a simple drop size distribution column model and Micro Rain Radar observations

Rainfall evaporation beneath cloud base level is a potential factor causing sub estimation of weather radar quantitative precipitation estimates (QPE), particularly at mid and long ranges in arid or semi-arid conditions. This effect is studied using observational data from the “Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment” (LIAISE) field campaign, part of the Global Energy and Water Exchanges (GEWEX) programme, which took place in the Eastern Ebro basin (NE Spain) in 2021. The objective of the study is to assess rainfall evaporation comparing a simple model with field campaign Micro Rain Radar (MRR) observations during LIAISE. The model describes the temporal evolution on a column of a drop size distribution (DSD) considering both sedimentation and evaporation. Ground based automated surface observations collocated with an MRR and a PARSIVEL disdrometer at three sites were used to identify possible events of rainfall evaporation (with precipitation and low relative humidity) and MRR data was processed with the RaProM and RaProM-Pro software (https://doi.org/10.3390/rs12244113, https://doi.org/10.3390/rs13214323) to compute radar reflectivity Z, liquid water content LWC, or precipitation type. Profiles of Z and LWC were examined with Contour Frequency Analysis Diagrams and the simple DSD column model. The case study shows the evolution of observed vs modelled DSDs with and without considering evaporation effects. Results indicated clearly the importance of including the evaporation to describe the evolution of the DSD during the event. This study was supported by Spanish projects WISE-PreP (RTI2018-098693-B-C32), ARTEMIS (PID2021-124253OB-I00) and the Water Research Institute (IdRA) of the University of Barcelona.