Evaluation of gridded rain‐gauge‐based precipitation datasets: impact of station density, spatial resolution, altitude gradient and climate

Gridded precipitation datasets have been developed for data assimilation and evaluation tasks of weather and climate models and for climate analyses. Gridded data uncertainty evaluation is crucial to understand the limitations and feasibility. The development of high‐resolution daily gridded precipitation datasets is desirable, but several factors need to be considered, namely rain gauge station availability, their spatial distribution, and orographic and climate characteristics of a study area. Quality assessment of gridded datasets can present difficulties when the influence of these factors is not thoroughly analysed. The main objective of this study was a detailed validation of precipitation grids based on four factors, that is, station density used for grid construction, grid spatial resolution, station altitude, and climate type. To this end, 18 grids were built using six spatial resolutions (0.01°, 0.025°, 0.05°, 0.1°, 0.2° and 0.4°) and three station densities (25, 50 and 75% of all available stations). Results indicate larger differences among the grids as a function of analysed factors. Station density was found to be the main factor, whereas grid spatial resolution had minor importance. However, the latter factor becomes more relevant in areas with strong altitude gradients and when a high station density is available. In addition, weak and moderate precipitation is overestimated on daily grids, whereas heavy precipitation cells are less frequent, reducing data variability. On the contrary, monthly and annual aggregates present less deviation from the observed distribution than daily comparisons. These findings question the applicability of the daily grid datasets for validation studies and climate analysis on a grid cell level.Funding came from projects LE240P18 (Consejería de Educación, Junta de Castilla y León) and CGL2016‐78702‐C2‐1‐R, PID2019‐108470RB‐C22, CGL2016‐80609‐R and PID2019‐108470RB‐C21 (Ministerio de Economía y Competitividad)

The contribution of rain gauges in the calibration of the IMERG product: results from the first validation over Spain

After 5 years in orbit, the Global Precipitation Measurement (GPM) mission has produced enough qualitycontrolled data to allow the first validation of their precipitation estimates over Spain. High-quality gauge data from the meteorological network of the Spanish Meteorological Agency (AEMET) are used here to validate Integrated Multisatellite Retrievals for GPM (IMERG) level 3 estimates of surface precipitation. While aggregated values compare notably well, some differences are found in specific locations. The research investigates the sources of these discrepancies, which are found to be primarily related to the underestimation of orographic precipitation in the IMERG satellite products, as well as to the number of available gauges in the GPCC gauges used for calibrating IMERG. It is shown that IMERG provides suboptimal performance in poorly instrumented areas but that the estimate improves greatly when at least one rain gauge is available for the calibration process. A main, generally applicable conclusion from this research is that the IMERG satellite-derived estimates of precipitation are more useful (r2 > 0.80) for hydrology than interpolated fields of rain gauge measurements when at least one gauge is available for calibrating the satellite product. If no rain gauges were used, the results are still useful but with decreased mean performance (r2 ~ 0.65). Such figures, however, are greatly improved if no coastal areas are included in the comparison. Removing them is a minor issue in terms of hydrologic impacts, as most rivers in Spain have their sources far from the coast.Funding from projects CGL2013- 48367-P, CGL2016-78702-C2-1-R, CGL2016-80609-R (Ministerio de Economía y Competitividad), UNCM08-1E-086 (Ministerio de Ciencia e Innovación), and Development of Numerical Weather Prediction and Data Application Technique 1365002970/KMA2018-00721 (Korea Meteorological Administration) is gratefully acknowledged

The September 2019 floods in Spain: An example of the utility of satellite data for the analysis of extreme hydrometeorological events

Major floods in Spain in September 9–13, 2019 resulted in seven casualties and massive losses to agriculture, property and infrastructure. This paper investigates the utility of satellite data to: (1) characterize the event when input into a hydrological model, and to provide an accurate picture of the evolution of the floods; and (2) inform meteorologists in real time in order to complement model forecasts. It is shown that the precipitation estimates from the Global Precipitation Measurement (GPM) Core Observatory (GPM-CO, available since 2014) and the merged satellite estimates provide an extraordinary improvement over previous technologies to monitor severe hydrometeorological episodes in near real time. In spite of known biases and errors, these new satellite precipitation estimates can be of broad practical interest to deal with emergencies and long-term readiness, especially for semi-arid areas potentially affected by ongoing global warming. Comparisons of satellite data of the September event with model outputs and more direct observations such as rain gauges and ground radars reinforce the idea that satellites are fundamental for an appropriate management of hydrometeorological events.Funding from projects PID2019-108470RB-C21, PID2019-108470RB-C22 (AEI/FEDER, UE), CGL2016-80609-R, and 1365002970/KMA2018-00721 (Korean Meteorological Agency, Korea) is gratefully acknowledged

A comparison of the First View of GPM with Ground Radar and NWCSAF CRPh over Continental Spain

Póster presentado en NWCSAF 2015 Users Workshop. 24-26 de febrero de 2015, MadridThe first, preliminary, data from the Global Precipitation Measurement Core Satellite illustrate the potential of this spacecraft for science and societal applications. Here we show a glimpse on the first overpasses over Spain. The DPR measurements and the GMI estimates area qualitatively compared with Ground Radar (GR) measurements from the National Radar Network of Spain (PPI); with EUMESAT NWCSAF Convective Rainfall Rate from Cloud Physical Properties (CRPh, based on VIS and IR: day-only product); and with Meteosat imagery (HRV and 10.8 mm IR channels from MSG). Notwithstanding the provisional character of the data and all the applicable caveats and isclaimers, both the GPM radar and the radiometer provide precipitation estimates that are remarkably close to ground radar observations. This is specially noticeable for the GMI, as the estimates used here come from the original, day-1 database. Also CRPh product shows a good behavior in all cases. The adequacy of using GPM data to calibrate/validate the NWCSAF CRPh product is being studied