• Capability of a regional climate model to simulate climate variables requested for water balance computation: a case study over northeastern France

D Boulard, T Castel, P Camberlin, AS Sergent, N Bréda, V Badeau, A Rossi & B Pohl.
Paru dans Climate Dynamics (DOI: 10.1007/s00382-015-2724-9)

• Climatic gradients along the windward slopes of Mount Kenya and their implication for crop risks. Part 2: crop sensitivity

Philippon, N., Baron, C., Boyard-Micheau, J., Adde A., Leclerc, C., Mwongera, C., Camberlin, P.

à paraître dans International Journal of Climatology

• Intra-seasonal rainfall variability over Madagascar 

Macron C, Y Richard, T Garot, M Bessafi, B Pohl, A Ratiarison, A Razafindrabe

à paraître dans Monthly Weather Review

Capability of a regional climate model to simulate climate variables requested for water balance computation: a case study over northeastern France

par D Boulard, T Castel, P Camberlin, AS Sergent, N Bréda, V Badeau, A Rossi & B Pohl. 
Paru dans Climate Dynamics (DOI: 10.1007/s00382-015-2724-9)

This paper documents the capability of the ARW/WRF regional climate model to regionalize near-surface atmospheric variables at high resolution (8 km) over Burgundy (northeastern France) from daily to interannual timescales. To that purpose, a 20-year continuous simulation (1989–2008) was carried out. The WRF model driven by ERA-Interim reanalyses was compared to in situ observations and a mesoscale atmospheric analyses system (SAFRAN) for five near-surface variables: precipitation, air temperature, wind speed, relative humidity and solar radiation, the last four variables being used for the calculation of potential evapotranspiration (ET0). Results show a significant improvement upon ERA-Interim. This is due to a good skill of the model to reproduce the spatial distribution for all weather variables, in spite of a slight over estimation of precipitation amounts mostly during the summer convective season, and wind speed during winter. As compared to the Météo-France observations, WRF also improves upon  SAFRAN analyses, which partly fail at showing realistic spatial distributions for wind speed, relative humidity and solar radiation—the latter being strongly underestimated. The SAFRAN ET0 is thus highly under-estimated too. WRF ET0 is in better agreement with observations In order to evaluate WRF’s capability to simulate a reliable ET0 , the water balance of thirty Douglas-fir stands was computed using a process-based model. Three soil water deficit indexes corresponding to the sum of the daily deviations between the relative extractible water and a critical value of 40 % below which the low soil water content affects tree growth, were calculated using the nearest weather station, SAFRAN analyses weather data, or by merging observation and WRF weather variables. Correlations between Douglas-fir growth and the three estimated soil water deficit indexes show similar results. These results showed through the ET0 estimation and the relation between mean annual SWDI and Douglas-fir growth index that the main difficulties of the WRF model to simulate soil water deficit is mainly attributable to its precipitation biases. In contrast, the low discrepancies between WRF and observations for air temperature, wind speed,relative humidity and solar radiation make then usable for the water balance and ET0 computation.

Climatic gradients along the windward slopes of Mount Kenya and their implication for crop risks. Part 2: crop sensitivity

par Philippon, N., Baron, C., Boyard-Micheau, J., Adde A., Leclerc, C., Mwongera, C., Camberlin, P.

à paraître dans international Journal of Climatology

Mount Kenya is an equatorial mountain whose climatic setting is fairly simple (two rainy seasons in March–May, the Long Rains, and October–December, the Short Rains) though concealing significant spatial variations related to elevation and aspect (part I, Camberlin et al., 2014). This part II is dedicated to the sensitivity of sorghum yields to climate variability in space and time, with a focus on the intra-seasonal characteristics of the rainy seasons. To that aim we use the crop model SARRA-H calibrated for the region and fed with rainfal , temperature, wind speed, humidity and solar radiation data over the period 1973–2001 at three stations located on the eastern slopes of Mount Kenya. The crop model is run independently for the two rainy seasons. Four groups of simulations are conducted by varying the initialization date of the simulation, the sowing dates and the type of soil, in order to test sorghum sensitivity to water availability. Evidence is found that potential sorghum yields are dominantly controlled by variations in seasonal rainfall amounts: mean yields are higher at higher and wetter locations, and are higher during the wettest rainy season and years. However, beyond this apparent simplicity, more complex aspects emerge of the crop–climate relationships. First, the yield–elevation relationship is altered at high elevation due to lower temperature. Second, despite a strong link with the seasonal rainfall amounts, we evidence an underlying role of some intra-seasonal rainfall characteristics such as the number of rainy days (itself mainly determined by the rainy season duration) or the occurrence of long dry spells. Third, unseasonal rains occurring after the end of the rainy season, especially after the Short Rains, play a role in final crop yield. Fourth, variations of climate variables such as solar radiation by modulating the potential evapotranspiration concur to yield variations at the wettest locations.

Intra-seasonal rainfall variability over Madagascar

 

par Macron C, Y Richard, T Garot, M Bessafi, B Pohl, A Ratiarison, A Razafindrabe

à paraître dans Monthly Weather Review

Using daily rain-gauge records for Madagascar and nearby islands, this paper investigates rainfall intraseasonal variability at local and regional scales during the austral summer season (November-February), as well as the respective influences of recurrent convective regimes over the South-West Indian Ocean (SWIO) and the Madden-Julian Oscillation (MJO). Our results show a general consistency between local-scale rainfall variability in Madagascar and regional-scale features of climate variability. The influence of Tropical-Temperate Troughs in their mature phase and/or their easternmost locations is first underlined. The development of such systems over Southern Africa and the Mozambique Chanel can be considered as precursors for Malagasy wet spells, especially over the southern part of the island. Regional and local effects of the MJO are weaker on average, and only concern the northwest of the island and the north of the Mozambique Chanel. MJO and convective regimes are finally shown to explain distinct fractions of regional rainfall variability.

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• Capability of a regional climate model to simulate climate variables requested for water balance computation: a case study over northeastern France

 

D Boulard, T Castel, P Camberlin, AS Sergent, N Bréda, V Badeau, A Rossi & B Pohl.
Paru dans Climate Dynamics (DOI: 10.1007/s00382-015-2724-9)

 

• Climatic gradients along the windward slopes of Mount Kenya and their implication for crop risks. Part 2: crop sensitivity

 

Philippon, N., Baron, C., Boyard-Micheau, J., Adde A., Leclerc, C., Mwongera, C., Camberlin, P.

 

à paraître dans International Journal of Climatology

 

 

• Intra-seasonal rainfall variability over Madagascar 

 

Macron C, Y Richard, T Garot, M Bessafi, B Pohl, A Ratiarison, A Razafindrabe

 

à paraître dans Monthly Weather Review

 

 

Capability of a regional climate model to simulate climate variables requested for water balance computation: a case study over northeastern France

 

par D Boulard, T Castel, P Camberlin, AS Sergent, N Bréda, V Badeau, A Rossi & B Pohl. 
Paru dans Climate Dynamics (DOI: 10.1007/s00382-015-2724-9)

 

This paper documents the capability of the ARW/WRF regional climate model to regionalize near-surface atmospheric variables at high resolution (8 km) over Burgundy (northeastern France) from daily to interannual timescales. To that purpose, a 20-year continuous simulation (1989–2008) was carried out. The WRF model driven by ERA-Interim reanalyses was compared to in situ observations and a mesoscale atmospheric analyses system (SAFRAN) for five near-surface variables: precipitation, air temperature, wind speed, relative humidity and solar radiation, the last four variables being used for the calculation of potential evapotranspiration (ET0). Results show a significant improvement upon ERA-Interim. This is due to a good skill of the model to reproduce the spatial distribution for all weather variables, in spite of a slight over estimation of precipitation amounts mostly during the summer convective season, and wind speed during winter. As compared to the Météo-France observations, WRF also improves upon  SAFRAN analyses, which partly fail at showing realistic spatial distributions for wind speed, relative humidity and solar radiation—the latter being strongly underestimated. The SAFRAN ET0 is thus highly under-estimated too. WRF ET0 is in better agreement with observations In order to evaluate WRF’s capability to simulate a reliable ET0 , the water balance of thirty Douglas-fir stands was computed using a process-based model. Three soil water deficit indexes corresponding to the sum of the daily deviations between the relative extractible water and a critical value of 40 % below which the low soil water content affects tree growth, were calculated using the nearest weather station, SAFRAN analyses weather data, or by merging observation and WRF weather variables. Correlations between Douglas-fir growth and the three estimated soil water deficit indexes show similar results. These results showed through the ET0 estimation and the relation between mean annual SWDI and Douglas-fir growth index that the main difficulties of the WRF model to simulate soil water deficit is mainly attributable to its precipitation biases. In contrast, the low discrepancies between WRF and observations for air temperature, wind speed,relative humidity and solar radiation make then usable for the water balance and ET0 computation.

 

Climatic gradients along the windward slopes of Mount Kenya and their implication for crop risks. Part 2: crop sensitivity

 

par Philippon, N., Baron, C., Boyard-Micheau, J., Adde A., Leclerc, C., Mwongera, C., Camberlin, P.

 

à paraître dans international Journal of Climatology

 

Mount Kenya is an equatorial mountain whose climatic setting is fairly simple (two rainy seasons in March–May, the Long Rains, and October–December, the Short Rains) though concealing significant spatial variations related to elevation and aspect (part I, Camberlin et al., 2014). This part II is dedicated to the sensitivity of sorghum yields to climate variability in space and time, with a focus on the intra-seasonal characteristics of the rainy seasons. To that aim we use the crop model SARRA-H calibrated for the region and fed with rainfal , temperature, wind speed, humidity and solar radiation data over the period 1973–2001 at three stations located on the eastern slopes of Mount Kenya. The crop model is run independently for the two rainy seasons. Four groups of simulations are conducted by varying the initialization date of the simulation, the sowing dates and the type of soil, in order to test sorghum sensitivity to water availability. Evidence is found that potential sorghum yields are dominantly controlled by variations in seasonal rainfall amounts: mean yields are higher at higher and wetter locations, and are higher during the wettest rainy season and years. However, beyond this apparent simplicity, more complex aspects emerge of the crop–climate relationships. First, the yield–elevation relationship is altered at high elevation due to lower temperature. Second, despite a strong link with the seasonal rainfall amounts, we evidence an underlying role of some intra-seasonal rainfall characteristics such as the number of rainy days (itself mainly determined by the rainy season duration) or the occurrence of long dry spells. Third, unseasonal rains occurring after the end of the rainy season, especially after the Short Rains, play a role in final crop yield. Fourth, variations of climate variables such as solar radiation by modulating the potential evapotranspiration concur to yield variations at the wettest locations.

Intra-seasonal rainfall variability over Madagascar

 

 
par Macron C, Y Richard, T Garot, M Bessafi, B Pohl, A Ratiarison, A Razafindrabe

 

à paraître dans Monthly Weather Review

 

Using daily rain-gauge records for Madagascar and nearby islands, this paper investigates rainfall intraseasonal variability at local and regional scales during the austral summer season (November-February), as well as the respective influences of recurrent convective regimes over the South-West Indian Ocean (SWIO) and the Madden-Julian Oscillation (MJO). Our results show a general consistency between local-scale rainfall variability in Madagascar and regional-scale features of climate variability. The influence of Tropical-Temperate Troughs in their mature phase and/or their easternmost locations is first underlined. The development of such systems over Southern Africa and the Mozambique Chanel can be considered as precursors for Malagasy wet spells, especially over the southern part of the island. Regional and local effects of the MJO are weaker on average, and only concern the northwest of the island and the north of the Mozambique Chanel. MJO and convective regimes are finally shown to explain distinct fractions of regional rainfall variability.