TRENDS AND CHANGE IN CLIMATE OVER THE VOLTA RIVER BASIN

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1 TRENDS AND CHANGE IN CLIMATE OVER THE VOLTA RIVER BASIN VOLTRES PROJECT WORK PACKAGE 1a: CLIMATE KEY RESULTS E. Obuobie, H.E. Andersen, C. Asante-Sasu, M. Osei-owusu 11/9/217

2 OBJECTIVES Analyse long term historical climate trends over the Volta Basin; and Generate and analyse downscaled future climate projections over the basin for use in impact analysis

3 STUDY AREA Volta Basin (Lake region verses upstream catchment) VBA - Volta Basin Portal, 215

4 STUDY AREA 85 climate stations 49 observed stations 36 virtual stations

5 DATA Data type Specific data Data period Resolution Data sources Observed climate time series Modeled climate time series Rainfall, Tmax, Tmin Rainfall, Tmax, Tmin Daily GMET & BFMET Daily CORDEX 1 -AFRICA (Giorgi et al. 29) Semi-observed rainfall time series (CHIRPS 2 ) Rainfall Daily (.5 o x.5 o ) Climate Hazard Group (Funk, et al., 214) Re-analysis data Rainfall, Tmax, Tmin Daily (.5 o x.5 o ) WFDEI 3 (Weedon et al., 2114) 1. CORDEX - Coordinated Regional Downscaling Experiment 2. CHIRPS - Climate Hazards Group InfraRed Precipitation with Stations 3. WFDEI - WATCH-Forcing-Data-ERA-Interim

6 DATA List of RCMs and driving GCMs that provided climate projection for the study Model name Model type Modelling Centre Reference SMHI-RCA4 CLMcom- CCLM RCM RCM Swedish Meteorological and Hydrological Institute Panitz et al. (213) Rockel et al. (28) MPI-ESM-LR GCM Max Planck Institute for Meteorology Popke et al. (213) EC-EARTH GCM EC-EARTH consortium Hazeleger et al. (21) CNRM-CM5 GCM Centre National de Recherches Météorologiques/Centre Européen de Recherche et Formation Avancée en Calcul Scientifique Voldoire et al. (212) Previous studies (e.g. Panitz et al., 214; Kim et al., 213, Dosio et al., 215; Klutse et al., 214; Abiodun et al., 215) have shown that CORDEX RCMs simulate well the spatial and temporal distributions of rainfall over West Africa, though with some seasonal and sub-regional biases

7 DATA IPCC Scenarios 2 most recent IPCC emission scenarios: Representative Concentration Pathways (RCPs): RCP4.5, RCP8.5 RCP4.5: represents medium-low emission scenario RCP8.5: represents the high end emission scenario Name Radiative Forcing Concentration (ppm) Emissions Pathway RCP8.5 >8.5 W/m 2 in 21 >137 eq-co 2 in 21 Rising RCP4.5 ~4.5W/m 2 at the stabilization ~66 eq-co 2 at the stabilization Stabilization without level after 21 level after 21 overshoot Baseline/reference period: Future time horizon:

8 METHODS Downscaling/bias correction of modeled data Method: Quantile-Quantile transformation (Maraun et al., 21; Themeßl et al., 211; Amadou et al., 215; Sarr et al., 215) Trend analysis Magnitude and direction of trends computed with Sens slope estimator (Sen, 1968; Theil, 195) Statistical significance of trends estimated with Mann-Kendal test (Mann, 1945;Kendall, 1975) at 95% confidence level

9 METHODS - 2 Trend analysis in mean parameters & extreme events 2 mean climate parameters (annual rainfall, mean temperature) and 1 extreme events (5 temperature & 5 rainfall related) Index id Index name Definitions Units TN1p Cool nights Percentage of days when TN<1th percentile Days TX1p Cool days Percentage of days when TX<1th percentile Days TN9p Warm nights Percentage of days when TN>9th percentile Days TX9p Warm days Percentage of days when TX>9th percentile Days WSDI Warm spell duration indicator Annual count of days with at least 6 consecutive days when TX>9th percentile Days R2 Number of days above 2 mm Annual count of days when PRCP>=2 mm Days CWD CDD Consecutive wet days Consecutive dry days Maximum number of consecutive days with RR>=2 mm Maximum number of consecutive days with RR<1mm R99p Extremely wet days Annual total PRCP when RR>99 th percentile mm SDII Simple daily intensity index Annual total precipitation divided by the number of wet days (defined as PRCP>=1.mm) in the year Days Days mm

10 Rainfall (mm) Rainfall (mm) Rainfall (mm) KEY RESULTS - 2 Trends in annual rainfall over the Volta Basin Volta Basin : Rainfall Anomaly Trend : -5.2 mm per year Volta Basin: Rainfall Upper Volta : Rainfall Anomaly 2 Upper Volta: Ranifall trend Trend : -3.8 mm per year Lower Volta : Rainfall Anomaly Trend : -6.6 mm per year Lower Volta: rainfall trend

11 Deg. Celcius Deg. Celcius Deg. Celcius KEY RESULTS Trends in annual temperature over the Volta Basin 1. Volta Basin : Temperature Anomaly Trend : +.35 Deg. C per decade Upper Volta : Temperature Anomaly Trend : +.3 Deg. C per decade Lower Volta Basin: Temperature anomaly Trend : +.39 Deg. C per decade

12 KEY RESULTS Trends in extreme temperature indices TEMPERATURE INDICES HISTORIC ( ) RCP4.5 (251-28) RCP8.5 (251-28) Index Slope STD of slope P-Value Slope STD of slope P-Value Slope STD of slope P-Value TX1P days/decade days/decade days/decade TN1P days/decade days/decade days/decade TX9P days/decade days/decade days/decade TN9P days/decade days/decade days/decade WSDI days/decade days/decade days/decade.1 Index Positive (significant) (%) Positive (non-significant) (%) Negative (significant) (%) Negative (non-significant) (%) TX1P TN1P TX9P TN9P WSDI

13 KEY RESULTS Trends in extreme rainfall indices RAINFALL INDICES HISTORIC ( ) RCP4.5 (251-28) RCP8.5 (251-28) Index Slope mean P-Value Slope STD of slope P-Value Slope STD of slope P-Value R days/decade days/decade days/decade.776 CWD days/decade days/decade days/decade.511 R99p %/decade %/decade %/decade.77 SDII mm/ decade mm/decade mm/ decade.798 CDD days/decade days/decade days/decade.636 Index Positive (significant) (%) Positive (non-significant) (%) Negative (significant) (%) Negative (non-significant) (%) R2 CWD R99p SDII CDD

14 Temperature ( o C) Temperature ( o C) Temperature ( o C) KEY RESULTS Projected maximum temperature over the Volta Basin from Upper Volta Basin (upstream of Lake Volta): Maximum Temperature ( o C) RCP4.5: +2.6 o C RCP8.5: +4.7 o C RCP4.5: +2.6 o C RCP8.5: +4.7 o C Volta Basin : Maximum Temperature ( o C) RCP4.5 RCP8.5 ENS-MEAN4.5 ENS-MEAN8.5 MODEL-HISTORICAL RCP4.5 RCP8.5 ENS-MEAN4.5 ENS-MEAN8.5 MODEL-HISTORICAL Lower Volta Basin (Region of Lake Volta): Maximum Temperature ( o C) RCP4.5: +2.7 o C RCP8.5: +4.7 o C CCLM-CNRM4.5 CCLM-CNRM8.5 ENS-MEAN4.5 ENS-MEAN8.5 MODEL-HISTORICAL ENS-M-MEAN OBSERVED

15 Temperature ( o C) Temperature (oc) Temperature (oc) KEY RESULTS Projected minimum temperature over the Volta Basin from RCP4.5: +2.5 o C RCP8.5: +3.5 o C Volta Basin :Minimum Temperature ( o C) RCP4.5 RCP8.5 ENS-MEAN4.5 ENS-MEAN8.6 MODEL-HISTORICAL ENS-M-MEAN Upper Volta Basin (upstream of Lake Volta): Minimum Temperature ( o C) RCP4.5: +2.6 o C RCP8.5: +3.8 o C RCP4.5 RCP8.5 ENS-MEAN4.5 ENS-MEAN8.6 MODEL-HISTORICAL ENS-M-MEAN Lower Volta Basin (Region of Lake Volta): Minimum Temperature ( o C) RCP4.5: +2.4 o C RCP8.5: +3.1 o C RCP4.5 RCP8.5 ENS-MEAN4.5 ENS-MEAN8.5 MODEL-HISTORICAL ENS-M-MEAN OBSERVED

16 KEY RESULTS Projected annual changes in mean temperature for , relative to Volta Basin Upper Volta Lower Volta Tmeam Scenario MIN MAX ENS-MEAN RCP RCP RCP RCP RCP RCP

17 Deg. Celcius Deg. Celcius Deg. Celcius KEY RESULTS Projected monthly temperature over the Volta Basin 4 Volta Basin: Tmean RCP4.5: RCP4.5: Historical: Observational: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 4 Upper Volta Basin: Tmean 4 Lower Volta Basin: Tmean RCP4.5: RCP8.5: Observational: Historical: RCP4.5: RCP8.5: Observational: Historical: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

18 Rainfall mm) Rainfall mm) Rainfall (mm) KEY RESULTS Projected annual rainfall over the Volta Basin for Volta Basin : Annual Rainfall (mm) RCP8.5 RCP4.5 ENS-MEAN8.5 ENS-MEAN4.5 MODEL-HISTORICAL OBS-MEAN ENS-M-MEAN Upper Volta Basin (upstream of Lake Volta): Annual Rainfall (mm) RCP8.5 RCP4.5 ENS-MEAN8.5 ENS-MEAN4.5 MODEL-HISTORICAL ENS-M-MEAN OBS-MEAN Lower Volta Basin (Region of Lake Volta) RCP8.5 RCP4.5 ENS-MEAN8.5 ENS-MEAN4.5 MODEL-HISTORICAL

19 Rainfall Amounr (mm) Rainfall Amounr (mm) KEY RESULTS Projected monthly rainfall over the Volta Basin 25 2 Upper Volta Basin (upstream of Lake Volta): Monthly Rainfall RCP4.5: RCP8.5: Observation: Historical: Lower Volta Basin (Region of Lake Volta): Monthly Total Rainfall RCP4.5: RCP8.5: Model-Historical: Observation: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

20 KEY RESULTS Projected annual changes in annual rainfall for , relative to Volta Basin Upper Volta Lower Volta Rainfall (%) Scenario RANGE ENS-MEAN RCP to RCP to RCP to RCP to RCP to RCP to Similar findings have been obtained by Sylla et al. 216; IPCC 213; Ly et al. 213; Druyan 211; Giorgi et al. 21; Sylla et al. 215;

21 CONCLUSIONS The Volta River Basin has experienced a statistically significant increase of about 1.6 o C (about.35 o C/decade) in the mean temperature from 1961 to 25. The rate of warming was faster in the region of Lake Volta, compared to the upstream catchment areas. The warming is projected to exacerbate by the end of the 21 st century, with projected increases of 1.4 o C to 2.5 o C and 2.2 o C to 3.2 o C for , relative to , for RCP4.5 and RCP8.5, respectively. The basin has experienced significant reduction (average of 5 mm per year) in annual rainfall in the period, the Lake region experienced a higher reduction compared to the upstream areas. In recent times, from 1981 to date, the rainfall has been on recovery even though not yet at the levels of the 196s. There is high variability and uncertainty regarding the trend of future rainfall over the basin. Model projections indicate a change of -23% to +2%, with a mean of about +2% for the two RCPs.

22 THANK YOU

Karonga Climate Profile: Full Technical Version

Karonga Climate Profile: Full Technical Version Prepared by: University of Cape Town November 2017 For enquiries regarding this Climate Profile, please contact Lisa van Aardenne (lisa@csag.uct.ac.za) or