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The influence of topography and land cover on air temperature space-time variability is examined in an urban environment with contrasted topography through simple and multiple linear regression (SLR and MLR) models, ran for each hour of the period 2014–2021, to explain spatial patterns of air temperature measured by a dense network. The SLR models reveal a complementary influence of topography and land cover, with the largest influence during daytime and nighttime, respectively. The MLR significantly improves upon the SLR models despite persistent intensity errors at night and spatial errors in the early morning. Topography influences air temperatures all year round, with temperature decreasing with height during the day and frequent thermal inversions at night (up to 30% of the time). Impervious surfaces are more influential in summer and early fall, especially during the late afternoon for the fraction covered by buildings and during the early night for the distance from the city centre. They contribute to increase air temperature close to the city centre and where the fraction covered by buildings is large. By contrast, vegetation contributes to cool air temperature during the night, especially in spring and early summer for field crops, summer and early fall for forests, and late fall and winter for low vegetation. Our framework proves to be a low-cost and efficient way to assess how strongly and how recurrently the static surface conditions influence air temperature along the annual and diurnal cycles. It is easily transposable to other areas and study fields. [ABSTRACT FROM AUTHOR]

Very little research has documented the exposure of populations in Africa to extreme heat. We measured indoor air temperature and humidity hourly for 13 months in seven houses of contrasted architecture and construction materials all in the northern neighbourhoods of Ouagadougou, Burkina Faso. These measurements are compared to air temperatures recorded at the synoptic weather station of Ouagadougou airport and to land surface temperature estimates from Landsat satellite images at seven dates with clear-sky conditions. The results reveal huge temperature differences (exceeding 10 °C) between houses, especially in the afternoon hours of the warmest season. Indoor temperature is also much more variable than land surface (outdoor) temperature in the same locations, as estimated by satellite imagery. Houses with greater thermal inertia smooth the afternoon temperature peak, reducing heat exposure. Heat stress bioindicators reveal that danger thresholds, while rarely reached in some houses, are frequently exceeded in others year round except for the core of the cold winter season (December and January). In spring, the hottest season, the danger threshold is almost permanently exceeded in these dwellings, exposing their inhabitants to significant heat stress. This pilot study shows the primary role of housing in modulating indoor temperature, raising questions of public health and habitability of Sahelian regions in a warming world. This issue will be of increasing importance with ongoing climate change, hence the need for further, more detailed instrumented campaigns in African settlements. Highlights: 1. Indoor temperatures vary tremendously between houses. 2. Contrasts between houses are greatest in the hottest hours of the warm season. 3. Thermal danger or extreme danger levels are often exceeded in some houses. 4. In some houses, heat stress may occur in all seasons except winter. 5. More instrumented campaigns for heat stress in African housing are needed. [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]

El Niño Southern Oscillation (ENSO) and given phases of the Madden-Julian Oscillation (MJO) show similar regional signatures over the Equatorial Indian Ocean, consisting in an enhancement or reversing of the convective and dynamic zonal gradients between East Africa and the Maritime Continent of Indonesia. This study analyses how these two modes of variability add or cancel their effects at their respective timescales, through an investigation of the equatorial cellular circulations over the central Indian Ocean. Results show that (1) the wind shear between the lower and upper troposphere is related to marked regional rainfall anomalies and is embedded in larger-scale atmospheric configurations, involving the Southern Oscillation; (2) the intraseasonal (30-60 days) and interannual (4-5 years) timescales are the most energetic frequencies that modulate these circulations, confirming the implication of the MJO and ENSO; (3) extreme values of the Indian Ocean wind shear result from the combination of El Niño and the MJO phase enhancing atmospheric convection over Africa, or La Niña and the MJO phase associated with convective activity over the Maritime Continent. Consequences for regional rainfall anomalies over East Africa and Indonesia are then discussed. [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]