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This study aims at investigating for the first time the links of daily rainfall over Tunisia to large-scale atmospheric conditions by establishing a weather regime (WR) classification over a North African-Mediterranean domain mostly encompassing North Africa. Seven WRs are identified in the year-round ERA-Interim (ERA-I) Mean Sea Level Pressure field spanning 1992–2011. This classification then served as reference to determine WRs in a WRF 10-member ensemble and a regional climate simulations ensemble from Euro-Cordex all driven by ERA-I. Capabilities of both ensemble simulations in reproducing the ERA-I WRs main characteristics, and in reproducing the main features of observed rainfall over Tunisia from a high-resolution local observational dataset and two satellite-gauge merged rainfall products are evaluated for each WR. The models best reproduced the ERA-I two wintertime NAO-like WRs (WR1 and WR3). Better performances of the WRF ensemble and larger spread within the Euro-Cordex models are overall obtained in all WRs. Wet and extremely wet conditions are mainly observed north of Tunisia and seem to be primarily driven by WR5 and WR3 (partly by WR7) featuring strong negative MSLP anomalies and anomalous cyclonic circulation impacting Tunisia. Opposite atmospheric conditions associated with anomalously dry conditions however prevailing all over the country are particularly observed during WR1. Intensity and sign of the simulated rainfall errors over Tunisia, as well as the model uncertainties, as qualified by the Signal-to-Noise ratio, are regime-dependent. The highest (lowest) annual and DJF model errors among the two ensembles are frequently obtained during WR1 (WR3 and WR7) and are discussed with regard to the weakening (strengthening) of the lateral forcing's magnitude over Tunisia. Model uncertainties are lower in DJF than in JJA. Lateral and orographic forcings restricting inter-member or inter-model spread are mostly associated with WR3 and WR5 in winter. Internal variability of the simulated rainfall field within the WRF ensemble is however persistently smaller than the inter-model spread for all WRs and for all considered timescales. [ABSTRACT FROM AUTHOR]

The potential effects on the regional climate induced by partially immersing the arid pre-Saharan playa basin of Chott el-Jerid (south of Tunisia) are investigated by comparing two multi-year (1991–2011) sets of numerical simulations each consisting of ten-member ensemble and performed using the WRF regional climate model. The first WRF ensemble is performed under current land use and land cover, while the second is carried out after introducing a virtual large and shallow surface water reservoir (a lake) in Chott el-Jerid. The most pronounced effects generated by the artificial lake are circumscribed over its surface and slightly spread downwind to the other parts of the Chott. The lake has a clear moderating effect on near-surface air temperatures by increasing (decreasing) the wintertime (summertime) air temperatures. Sensible heat fluxes are remarkably increased in winter and decreased in summer over the lake following the temperature gradient between the lake surface and the overlying atmosphere. Latent heat fluxes, moisture convergence, and water vapor mixing ratio are increased over the lake throughout the year, especially in winter. The lake also induces domain-wide decreased (increased) surface pressures and land (lake) breeze circulation in winter (summer). Simulated rainfall amounts are most increased over the lake in winter likely because of an enhanced atmospheric instability, while they slightly decrease in summer. [ABSTRACT FROM AUTHOR]

Temporal and spatial variability of rainfall over Tunisia (at 12 km spatial resolution) is analyzed in a multi-year (1992-2011) ten-member ensemble simulation performed using the WRF model, and a sample of regional climate hindcast simulations from Euro-CORDEX. RCM errors and skills are evaluated against a dense network of local rain gauges. Uncertainties arising, on the one hand, from the different model configurations and, on the other hand, from internal variability are furthermore quantified and ranked at different timescales using simple spread metrics. Overall, the WRF simulation shows good skill for simulating spatial patterns of rainfall amounts over Tunisia, marked by strong altitudinal and latitudinal gradients, as well as the rainfall interannual variability, in spite of systematic errors. Mean rainfall biases are wet in both DJF and JJA seasons for the WRF ensemble, while they are dry in winter and wet in summer for most of the used Euro-CORDEX models. The sign of mean annual rainfall biases over Tunisia can also change from one member of the WRF ensemble to another. Skills in regionalizing precipitation over Tunisia are season dependent, with better correlations and weaker biases in winter. Larger inter-member spreads are observed in summer, likely because of (1) an attenuated large-scale control on Mediterranean and Tunisian climate, and (2) a larger contribution of local convective rainfall to the seasonal amounts. Inter-model uncertainties are globally stronger than those attributed to model's internal variability. However, inter-member spreads can be of the same magnitude in summer, emphasizing the important stochastic nature of the summertime rainfall variability over Tunisia. [ABSTRACT FROM AUTHOR]

In the original article, the last panel of Fig. 10 should be labeled "h". Also some data and Table 2 caption were unfortunately incorrect. [ABSTRACT FROM AUTHOR]