Seasonal precipitation variability in regional climate simulations over Northern basins of Tunisia

Abstract

Northern Tunisia is the rainiest part of the country where most of the water management structures (dams, reservoirs, etc) are located. Its strategic situation with respect to surface water resources encourages the investigation of the climate change impacts projected by climate models. The goal of this study is first to compare the observed precipitation with climate model outputs, and then to evaluate the future changes projected by different climate models. The study area is subdivided into four regions: the upstream and downstream transboundary Medjerda basin, the northern coastal basins and the eastern coastal basins. A database provided by the Tunisian hydrological service includes 388 stations with complete monthly precipitation data over the period 1961-2000. An ensemble of Regional Climate Models (RCM) simulations provided by the European Union-funded project ENSEMBLES are used. Six RCM model runs (CNR-A, DMI-A, DMI-B, ICT-E, SMH-B and SMH-E) are analysed, for the control period 1961-2000 and two projection periods, 2011-2050 and 2051-2090. The models efficiency in reproducing seasonal precipitation amounts and variability is evaluated. A 1-km monthly precipitation reference grid is computed through the interpolation of rainfall observations during the period 1961-2000 with kriging techniques. Monthly precipitation series averaged over the four basins are built for comparison during the control period. The RCM outputs are evaluated with respect to the annual precipitation cycle and rainfall frequency distribution using robust statistics. For the control period, features of the seasonal regimes are well reproduced by all models. It is found that models underestimate seasonal precipitation on average by 20%. The discrepancy between model outputs and observations depends on the season. For the future, in summer and autumn the different models do not project major changes in the seasonal distributions. However, for winter and spring, all the models project a significant decrease of precipitations.

Seasonal rainfall variability in the southern Mediterranean border: Observations, regional model simulations and future climate projections

“…Pettitt's test is one of the most non-parametric tests used to detect a rupture within time series of hydro-climatological data. Several studies have used this test to analyze rainfall variability in northern Algeria Bekkoussa et al, 2008;Meddi et al, 2010;Taibi et al, 2013;etc. studies have used this method for the same analysis (Tramblay et al, 2012;Bargaoui et al, 2014;Alemseged et al, 2015;Giménez et al, 2016;Hertig and Tramblay, 2016;Paeth et al, 2016).…”

“…The assessment of the impact of climate change on the hydrological variability of the Mediterranean basin using climate models has been widespread in river basins in France (Quintana Seguí et al, 2010), Spain (Majone et al, 2012;Giménez et al 2016), Italy (Senatore et al, 2011) and across the Mediterranean basin (Sánchez-Gómez et al, 2009;Dubois et al, 2012;Milano et al, 2012Milano et al, , 2013Hertig and Tramblay, 2016;Paeth et al, 2016;Alemseged and Tom, 2015). However, few studies have been interested in the details in North Africa (Driouech et al, 2010;Tramblay et al, 2012;Bargaoui et al, 2014;Filahi et al, 2017). Giorgio and Lionello (2008) analyzed rainfall data from the PRUDENCE climate model simulations in different regions of the Mediterranean basin (north, south, east, west, central).…”

“…For the Mediterranean stations, the projected changes are difficult to assess due to the great variability. In Tunisia, Bargaoui et al (2014) assessed the outputs of six ENSEMBLES models for the 1961-2000 control period and for two projection periods, 2011-2050 and 2051-2090. They found that, on average, the model outputs underestimate seasonal precipitation by 20%.…”

Climate change vulnerability, water resources and social implications in North Africa

“…Indeed, besides the trends in water supply, several studies project a strong increase in water demand for this region due to population growth and economic development, indicating a higher water stress in the future (e.g., Milano et al 2012). Some studies provide hydrological scenarios on the scale of individual basins in Algeria (e.g., Benhamiche et al 2014;Elmeddahi et al 2014), Morocco (e.g., Brouziyne et al 2018;Tramblay et al 2013b) and Tunisia (e.g., Bargaoui et al 2013;Dakhlaoui et al 2017). Their results indicate a decrease in surface flows that is more pronounced under the RCP8.5 than under the RCP4.5 scenario.…”

Hydrological Modeling in Northern Tunisia with Regional Climate Model Outputs: Performance Evaluation and Bias-Correction in Present Climate Conditions

“…This makes it important to consider the likely consequences of climate change on this resource. In particular, future climate projections for this area indicate a decrease in precipitation by 20% [4]. Such projections stress the need for impact studies at the basin scale, which is the relevant scale for water resource management and mitigation strategies.…”