Precipitation changes at the global level display a complex pattern, without a clear-cut average trend in the last century but with an apparent tendency to the intensification of the hydrological cycle in many areas of the world. Global climate models indicate possible global precipitation changes before the end of the century, with an intensity and pattern that depend on the specific climate scenario and are not always consistent between the different models.
Precipitation is a particularly difficult variable, as it is characterized by strong intermittency at all scales and strong orographic dependence, which makes it often hard to model and to measure (see Fig. 1). The measurement of precipitation itself, either by ground stations, radars or satellites, is still a challenging task, which becomes especially hard for solid precipitation at high latitudes or altitudes. These difficulties could hamper efforts to understand and model the hydrological cycle and its variability.
This research task intends to study current and expected changes of precipitation at the global and European scale, with a specific focus on extreme episodes and their effects on mean runoff and intense flooding and drought events.
Groups involved in ECRA participate in the Global Monitoring for Environment and Security (GMES) initiative, which aims at filling in the gaps of the current observing networks, and in the GEO/GEOSS programme.
The methods used in order to achieve the objectives of this task will be data analysis approaches and a host of different modelling methods:
Data-wise, the focus will be mainly on satellite data and their interpretation, including the problem of precipitation and snow cover retrieval and analysis, and on the study of long historical climatic time series from ground station networks. In particular, satellite data will be instrumental for the definition of water scarcity and drought conditions in connection with global and regional hydrological models in the relatively data sparse areas of the globe.
At the modelling level, global and regional climate models, mesoscale convective models and stochastic/statistical downscaling procedures, coupled with hydrological models of varying complexity and sub-surface water dynamics will be used and developed. A huge numerical initiative based on the use of high-resolution climate models coupled with global runoff and subsurface flow models will provide new and crucial information on how the global hydrological cycle is changing. Regional climate models nested into the global simulations will allow for focusing on specific climatic hotspots.
Figure 1 shows, as an example, a comparison between different gridded precipitation datasets of different origin (station data, satellite, climate model) for the HKKH area. Notice how the different observational datasets display significant differences from each other.
Figure 1. Multiannual mean (1998-2007) of summer (JJAS) precipitation over the region between 69° and 95°E and 23° and 39°N from the APHRODITE, CRU, GPCC, TRMM, GPCP, ERA-Interim and EC-Earth model datasets. From Palazzi et al., "Precipitation in the Hindu-Kush Karakoram Himalaya: observations and future scenarios", JGR-Atmospheres (2013).