Evaluation of precipitation variability over the Sierra de Guadarrama

Heterogeneity in the occurrence, amount, and distribution of precipitation in mountainous areas is relevant for water resources and stresses the need for high-altitude observations and high-resolution modeling over complex terrain. However, the harsh weather conditions and the complex terrain associated with these environments hinder a continuous monitorization and pose challenges for regional climate models.

In this work, data from 37 stations located in the Sierra de Guadarrama and nearly lowlands, in Central Spain, and with altitudes ranging from 600 to 2200 m.a.s.l. have been studied. A few of the highest altitude sites belong to GuMNet facility (https://www.ucm.es/gumnet) and the rest to the Spanish Meteorological Agency (AEMET; https://www.aemet.es). These data have been compared to ERA5 reanalysis (https://confluence.ecmwf.int/display/CKB/ERA5) and to three different resolution (9, 3, and 1 km) outputs of a simulation of the regional climate model WRF (https://www.mmm.ucar.edu/WRF) during the period from 1990-2019. The comparison of the different data sources aims at characterizing the precipitation distribution over the area, assessing the goodness of ERA5, and the potential added value of the increasing resolution of WRF simulation in reproducing the observations.

Results show that the increase in WRF resolution from 9 to 3 km always produces a better representation of precipitation, whereas the step from 3 to 1 km shows a significant improvement at the highest altitudes, but an overestimation of precipitation at low plain areas. The lack of added value in the simulation at the highest resolution is discussed in relation to the parameterization of cumulus precipitation. Also, an altitudinal gradient of precipitation is observed and can be traced to large-scale precipitation.