Malawi. General Climate. UNDP Climate Change Country Profiles. C. McSweeney 1, M. New 1,2 and G. Lizcano 1

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1 UNDP Climate Change Country Profiles Malawi C. McSweeney 1, M. New 1,2 and G. Lizcano 1 1. School of Geography and Environment, University of Oxford. 2. Tyndall Centre for Climate Change Research General Climate Malawi is located in eastern southern Africa, stretching across latitudes 9 15 S. The country s topography is highly varied; the Great Rift Valley runs North to South through the country, containing Lake Malawi, and the landscape around the valley consists of large at an elevation of around m, but with peaks as high as 3000m. The country s climate is tropical, but the influence of its high elevation means that temperatures are relatively cool. In winter (JJA) temperatures drop to around C, and in the warmest months (September to January) temperatures range from C. Wet season rainfalls depend on the position of the Inter tropical Convergence Zone (ITCZ) which can vary in its timing and intensity from year to year. In the south of Malawi the wet season normally lasts from November to February bringing around m per month, but rain continues into March and April in the north of the country as the ITCZ migrates northwards. Topographical influences also cause local variations to the rainfall with the highest altitude regions receiving the highest rainfalls. Inter annual variability in the wet season rainfall in Malawi is also strongly influenced by Indian Ocean Sea Surface Temperatures, which can vary from one year to another due to variations in patterns of atmospheric and oceanic circulation. The most well documented cause of this variability is the El Nino Southern Oscillation (ENSO). The influences of ENSO on the climate of Malawi can be difficult to predict as it sits between two regions of opposing climatic response to El Niño. Eastern equatorial Africa tends to receive above average rainfall in El Niño conditions, whilst south eastern Africa often experiences below average rainfall. The opposite response pattern occurs in La Niña episodes. The response of climate in each of these two regions, and the extent of the area affected, varies with each El Niño or La Niña event causing mixed responses in Malawi. 1

2 Recent Climate Trends Temperature Mean annual temperature has increased by 0.9 C between 1960 and 2006, an average rate of 0.21 C per decade. This increase in temperature has been most rapid in summer (DJF) and slowest in SON. Daily temperature observations show significantly increasing trends in the frequency hot days 1 and nights in all seasons. o The average number of hot days per year in Malawi has increased by 30.5 (an additional 8.3% of days 2 ) between 1960 and The rate of increase is seen most strongly in DJF when the average number of hot DJF days has increased by 3.9 days per month (an additional 12.7% of DJF days) over this period. o The average number of hot nights per year increased by 41 (an additional 11.1% of nights) between 1960 and The rate of increase is seen most strongly in DJF when the average number of hot DJF nights has increased by 5.5 days per month (an additional 17.6% of DJF nights) over this period. The frequency of cold days 3 and nights have decreased significantly since 1960 in all seasons except SON. o The average number of cold days per year has decreased by 16 (4.3% of days) between 1960 and This rate of decrease is most rapid in MAM when the average number of cold MAM days has decreased by 2.4 days per month (7.2% of MAM days) over this period. o The average number of cold nights per year has decreased by 33 (8.9% of days). This rate of decrease is most rapid in MAM when the average number of cold MAM nights has decreased by 3.2 nights per month (10.4% of MAM nights) over this period. Precipitation Year to year variability in rainfall is very string in Malawi and this can make it difficult to identify long term trends. Observations of rainfall over Malawi do not show statistically significant trends. Wet season (DJF) rainfall over Malawi in 2006 was particularly low, causing an apparent decreasing trend in DJF rainfall but there is no evidence of consistent decreases. There are no statistically significant trends in the extremes indices calculated using daily precipitation observations. 1 Hot day or hot night is defined by the temperature exceeded on 10% of days or nights in current climate of that region and season. 2 The increase in frequency over the 43 year period between 1960 and 2003 is estimated based on the decadal trend quoted in the summary table. 3 Cold days or cold nights are defined as the temperature below which 10% of days or nights are recorded in current climate of that region or season. 2

3 GCM Projections of Future Climate Temperature The mean annual temperature is projected to increase by 1.1 to 3.0 C by the 2060s, and 1.5 to 5.0 C by the 2090s. Under a single emissions scenario, the projected changes from different models span a range of up to 2.1 C. All projections indicate substantial increases in the frequency of days and nights that are considered hot in current climate. o Annually, projections indicate that hot days will occur on 14 32% of days by the 2060s, and 15 53% of days by the 2090s. o Nights that are considered hot for the annual climate of are projected to increase more quickly that hot days, occurring on 27 53% of nights by the 2060s and 31 72% of nights by the 2090s. Nights that are considered hot for each season by standards are projected to increase particularly rapidly in DJF, occurring on 47 99% of nights in every season by the 2090s. All projections indicate decreases in the frequency of days and nights that are considered cold in current climate. These events are expected to become exceedingly rare, and do not occur at all under the highest emissions scenario (A2) by the 2090s. Precipitation Projections of mean rainfall do not indicate substantial changes in annual rainfall. The range of projections from different models is large and straddles both negative and positive changes ( 13% to +32%). Seasonally, the projections tend towards decreases in dry season rainfall (JJA and SON), and increases in wet season rainfall (DJF and MAM). o Projected changes in JJA rainfall range from 77 to +48% with ensemble median changes of 5 to 18% and in SON, 63 to +40% with ensemble median values 7 to 20%. o Projected changes in DJF rainfall range from 8 to +25% with ensemble median changes of 4 to +11% and in MAM, 17 to +99% with ensemble median values of +1 to +7%) Overall, the models consistently project increases in the proportion of rainfall that falls in heavy events in the annual average under the higher emissions scenarios (A2 and A1B), of up to 19% by the 2090s. These increases mainly arise from increases in heavy events in the wetseasons, DJF and MAM, and are partially offset by decreases in JJA and SON. The models consistently project increases in 1 and 5 day rainfall maxima by the 2090s under the higher emissions scenarios, of up to 26mm in 1 day events, and 39mm in 5 day events. These also generally increase in DJF and MAM, but decrease in JJA and SON. 3

4 Other Regional Climate Change Information Model simulations show wide disagreements in projected changes in the amplitude of future El Niño events. Malawi s climate can be strongly influenced by ENSO, thus contributing to uncertainty in climate projections for this region. For further information on climate projections for Africa, see Christensen et al. (2007) IPCC Working Group I Report: The Physical Science Basis, Chapter 11 (Regional Climate projections): Section 11.2 (Africa). 4

5 Data Summary Observed Mean Observed Trend Projected changes by the 2030s Projected changes by the 2060s Projected changes by the 2090s Min Median Max Min Median Max Min Median Max Temperature ( C) (change in C per decade) Change in C Change in C Change in C A Annual * A1B B A DJF * A1B B A MAM * A1B B A JJA * A1B B A SON * A1B B Precipitation (mm per month) (change in mm per decade) Change in mm per month Change in mm per month Change in mm per month A Annual A1B B A DJF * A1B B A MAM A1B B A JJA A1B B A SON A1B B Precipitation (%) (mm per month) (change in % per decade) % Change % Change % Change A Annual A1B B A DJF * A1B B A MAM A1B B A JJA A1B B A SON A1B B

6 Observed Mean Observed Trend Projected changes by the 2030s Projected changes by the 2060s Projected changes by the 2090s Min Median Max Min Median Max Min Median Max % Frequency Change in frequency per decade Future % frequency Future % frequency Frequency of Hot Days (TX90p) A2 **** **** **** Annual * A1B **** **** **** B1 **** **** **** A2 **** **** **** DJF * A1B **** **** **** B1 **** **** **** A2 **** **** **** MAM * A1B **** **** **** B1 **** **** **** A2 **** **** **** JJA * A1B **** **** **** B1 **** **** **** A2 **** **** **** SON * A1B **** **** **** B1 **** **** **** Frequency of Hot Nights (TN90p) A2 **** **** **** Annual * A1B **** **** **** B1 **** **** **** A2 **** **** **** DJF * A1B **** **** **** B1 **** **** **** A2 **** **** **** MAM * A1B **** **** **** B1 **** **** **** A2 **** **** **** JJA * A1B **** **** **** B1 **** **** **** A2 **** **** **** SON * A1B **** **** **** B1 **** **** **** Frequency of Cold Days (TX10p) A2 **** **** **** Annual * A1B **** **** **** B1 **** **** **** A2 **** **** **** DJF A1B **** **** **** B1 **** **** **** A2 **** **** **** MAM * A1B **** **** **** B1 **** **** **** A2 **** **** **** JJA * A1B **** **** **** B1 **** **** **** A2 **** **** **** SON A1B **** **** **** B1 **** **** **** Frequency of Cold Nights (TN10p) A2 **** **** **** Annual * A1B **** **** **** B1 **** **** **** A2 **** **** **** DJF * A1B **** **** **** B1 **** **** **** A2 **** **** **** MAM * A1B **** **** **** B1 **** **** **** A2 **** **** **** JJA * A1B **** **** **** B1 **** **** **** A2 **** **** **** SON * A1B **** **** **** B1 **** **** ****

7 Observed Mean Observed Trend Projected changes by the 2030s Projected changes by the 2060s Projected changes by the 2090s Min Median Max Min Median Max Min Median Max % total rainfall falling in Heavy Events (R95pct) % Change in % per decade Change in % Change in % A2 **** **** **** Annual A1B **** **** **** B1 **** **** **** A2 **** **** **** DJF **** **** A1B **** **** **** B1 **** **** **** A2 **** **** **** MAM **** **** A1B **** **** **** B1 **** **** **** A2 **** **** **** JJA **** **** A1B **** **** **** B1 **** **** **** A2 **** **** **** SON **** **** A1B **** **** **** B1 **** **** **** Maximum 1 day rainfall (RX1day) mm Change in mm per decade Change in mm Change in mm A2 **** **** **** Annual **** **** A1B **** **** **** B1 **** **** **** A2 **** **** **** DJF A1B **** **** **** B1 **** **** **** A2 **** **** **** MAM A1B **** **** **** B1 **** **** **** A2 **** **** **** JJA A1B **** **** **** B1 **** **** **** A2 **** **** **** SON A1B **** **** **** B1 **** **** **** Maximum 5 day Rainfall (RX5day) mm Change in mm per decade Change in mm Change in mm A2 **** **** **** Annual A1B **** **** **** B1 **** **** **** A2 **** **** **** DJF A1B **** **** **** B1 **** **** **** A2 **** **** **** MAM A1B **** **** **** B1 **** **** **** A2 **** **** **** JJA A1B **** **** **** B1 **** **** **** A2 **** **** **** SON A1B **** **** **** B1 **** **** **** * indicates trend is statistically significant at 95% confidence **** indicates data are not available 7

8 Figure 1: Trends in annual and seasonal mean temperature for the recent past and projected future. All values shown are anomalies, relative to the mean climate. Black curves show the mean of observed data from 1960 to 2006, Brown curves show the median (solid line) and range (shading) of model simulations of recent climate across an ensemble of 15 models. Coloured lines from 2006 onwards show the median (solid line) and range (shading) of the ensemble projections of climate under three emissions scenarios. Coloured bars on the right-hand side of the projections summarise the range of mean climates simulated by the 15 models for each emissions scenario. 8

9 Figure 2: Spatial patterns of projected change in mean annual and seasonal temperature for 10-year periods in the future under the SRES A2 scenario. All values are anomalies relative to the mean climate of In each grid box, the central value gives the ensemble median and the values in the upper and lower corners give the ensemble maximum and minimum. 9

10 Figure 3: Trends in monthly precipitation for the recent past and projected future. All values shown are anomalies, relative to the mean climate. See Figure 1 for details. 10

11 Figure 4: Spatial patterns of projected change in monthly precipitation for 10-year periods in the future under the SRES A2 scenario. All values are anomalies relative to the mean climate of See Figure 2 for details. 11

12 Figure 5: Trends in monthly precipitation for the recent past and projected future. All values shown are percentage anomalies, relative to the mean climate. See Figure 1 for details. 12

13 Figure 6: Spatial patterns of projected change in monthly precipitation for 10-year periods in the future under the SRES A2 scenario. All values are percentage anomalies relative to the mean climate of See Figure 2 for details. 13

14 Figure 7: Trends in Hot-day frequency for the recent past and projected future. See Figure 1 for details. 14

15 Figure 8: Spatial patterns of projected change in Hot-day frequency for 10-year periods in the future under the SRES A2 scenario. See Figure 2 for details. 15

16 Figure 9: Trends in hot-night frequency for the recent past and projected future. See Figure 1 for details. 16

17 Figure 10: Spatial patterns of projected change in hot-night frequency for 10-year periods in the future under the SRES A2 scenario. See Figure 2 for details. 17

18 Figure 11: Trends in cold-day frequency for the recent past and projected future. See Figure 1 for details. 18

19 Figure 12: Spatial patterns of projected change in cold-day frequency for 10-year periods in the future under the SRES A2 scenario. See Figure 2 for details. 19

20 Figure 13: Trends in cold-night frequency for the recent past and projected future. See Figure 1 for details. 20

21 Figure 14: Spatial patterns of projected change in cold-night frequency for 10-year periods in the future under the SRES A2 scenario. See Figure 2 for details. 21

22 Figure 15: Trends in the proportion of precipitation falling in heavy events for the recent past and projected future. All values shown are anomalies, relative to the mean climate. See Figure 1 for details. 22

23 Figure 16: Spatial patterns of projected change in the proportion of precipitation falling in heavy events for 10-year periods in the future under the SRES A2 scenario. All values are anomalies relative to the mean climate of See Figure 2 for details. 23

24 Figure 17: Trends in maximum 1-day rainfall for the recent past and projected future. All values shown are anomalies, relative to the mean climate. See Figure 1 for details. 24

25 Figure 18: Spatial patterns of maximum 1-day rainfall for 10-year periods in the future under the SRES A2 scenario. All values are anomalies relative to the mean climate of See Figure 2 for details. 25

26 Figure 19: Trends in maximum 5-day rainfall for the recent past and projected future. All values shown are anomalies, relative to the mean climate. See Figure 1 for details. 26

27 Figure 20: Spatial patterns of projected change in maximum 5-day rainfall for 10-year periods in the future under the SRES A2 scenario. All values are anomalies relative to the mean climate of See Figure 2 for details. 27