Analysis of Hydro-climatology of Malawi Cosmo Ngongondo 2017 World Water Day, 20 March 2017, Mangochi, Malawi Department of Geography and Earth Sciences, Faculty of Science, University of Malawi, Chancellor College, P.O. Box 280, Zomba, Malawi Email: cngongondo@cc.ac.mw

Background Water resources availability at any temporal and spatial scales is governed by complex interactions between climate and hydrological processes Need: Analyse observed hydroclimatic parameters to inform future water availability Data Scarcity: A challenge in many parts of the developing world Need less data intensive approaches

20th Century runoff trends Fig. 1: Observation driven global runoff trends 1900-1999 Piao et al 2007, PNAS 25 , doi/10.107/pnas.0707213104

20th century river discharge trends Fig. 2: Observed river discharge trends during 1900-1999 Large catchments > 50,000 km2 Based on difference between 1900-1970 relative to 1971-1998 10-40% decreases in observed river discharge over southern Africa Milly et al 2005, Nature, 438, doi:10.1038/nature04312

Key Water Challenges in Southern Africa Rapid population and economic growth Expansion of irrigated agriculture Transboundary water transfers (Botswana and Namibia Ecological Needs Climate Change – potential for international water conflicts Beck & Bernauer (2011)

Study Aims Analyse the hydro-climatology of Malawi from 1971 to 2001 Model the water balance components (Rainfall, Temperature, Potential & Actual Evapotranspiration, Runoff Analyse their temporal trends Based on Ngongondo et al. (2015), Quart. International & Ngongondo et al. (2011), Theor. & Appd Climatology Compare the temporal patterns with Lake level and river flow response

Data and Methods Thornthwaite Monthly water balance model Model Inputs Monthly Rainfall Monthly Temperature Soil moisture capacity Latitude Outputs Potential ET Actual ET Runoff Time slice: 1971-2001 Fig. 3

Data Analysis Areal mean of standardised anomalies series Mann-Kendal statistic: trend direction and significance (a=0.05) (WMO Recommended) Slope: Linear Regression Station Water Balance values were Interpolated on Map of Malawi using ordinary Krigging

Climate Stations 28 Synoptic stations Fig. 4

Climate Stations Fig. 5

Summary of Malawi Hydro-Climate

Standardised anomalies series (1971-2001) Rainfall Temperature Runoff PET AET Contrasting patterns of PET and AET Fig. 5

Trends in monthly water balance Rainfall Temperature PET AET Runoff Fig. 6

Complimentary ET relationship ETp+ ETa= 2ETw Water limited environments Energy limited environments

Complimentary ET relationship ETw Radiative budget: increase results in both Eta and Etp increase Advective budget: increase results in decreased Eta and increased Etp Increase in water limitation as a result of the reduced rainfall

Lake Malawi Monthly Levels (1898-2017) 1899 to 1979/80 1915- 1935 Minimum=Dec 1915 (469.94 m) Maximum= May 1980 (477.2 m) Mean= 473.8 m 1978-2017

Lake Malawi Annual Levels (1898-2017) Mean= 473.8 m Maximum= 1979/80 (476.5 m) Minimum= 1914/14 (470.4 m) Significant positive MK trend, slope 0.035 m per year

Lake Malawi Monthly Levels (1898-1979) Minimum= Dec 1915 (469.9 m) Maximum= May 1979 (477.1 m) Mean= 473.3 m Significant Positive MK Trend with slope= 0.067 m per month

Lake Malawi Monthly Levels (1899-1979) Minimum= 1914/15 (473 m) Maximum= 1979/80 (476.4 m) Mean= 470.4 m Significant Positive trend with slope 0.067 m per year

Lake Malawi Monthly Levels (1979-Feb 2017) Minimum= Dec 1995 (473 m) Maximum= May 1980 (477.2 m) Mean= 474.8 m Significant Negative MK Trend , slope=-0.04 m per month

Lake Malawi Monthly Levels (1979-2016) Mean= 474.8 m Maximum=476.5 m Minimum=473.4 m Significant Negative MK trend, -0.048 m per year

Monthly lake Levels periodicity

Monthly lake Levels periodicity (Detrended Series)

Ruo River @ M1 Road Bridge Catchment area: 193 km2 Significant negative MK trend

Linthipe @ Kamuzu Bridge Significant negative MK trend

Summary Malawi’s Climate and hydrological cycle are intimately linked. Most projections show large parts of southern Africa are getting warmer- signficant temperature increase in Malawi Rainfall decreasing (not Significant) AET and Runoff following rainfall pattern- Moisture limitations Lake Malawi levels and some key river flows decreasing- Climate signal+ catchment processes+ noise

Thank you !