Namibian Experiences

Coping with Floods and Droughts UNESCO G-WADI Geo-Server use

Pauline Mufeti Namibia Hydrological Services

18 JUNE 2014 ,UNESCO-UCI ,G-WADI workshop

Namibian Climate • Arid to semi arid country

• Hydro – meteorological extremes- Floods – Droughts (hydrological droughts = low river flows)

Droughts Floods

integral part of Namibia’s inherent climatic

variability

Climate • Driest country in sub-Saharan Africa <- cold Benguela

current at Atlantic coast • Seasonal climate <-movement of Inter Tropical

Convergence Zone (ITCZ)

FLOODS AND DROUGHTS IN NAMIBIA CLIMATIC DRIVERS Rainfall Seasonal convective thundershowers in rainy season from October to April

Low with average range from virtually zero at coast to over 600 mm / year in far northeast

Highly variable (and unreliable)

within rainy season between rainy seasons

(Windhoek from less than 100 to more than 1,000 mm)

Evaporation High with average range from less than 2,000 mm / year at coast to over 3,400 mm / year in southeast Potential evapotranspiration exceeds rainfall by far -> arid to semi-arid conditions

Climate

projected median change in annual frequency of extreme rainfall events (> 20 mm/day) (from Climate Risk and Vulnerability – A Handbook for Southern Africa – http://www/rvatlas.org/sadc)

CGM models shows wide range of forecasted change magnitudes

There would be no tendency towards more (or less) frequent extreme rainfalls, and hence no tendency towards more frequent and higher floods for Namibia.

Climate • Historic hydro meteorological records, shows increased

temperatures but no changes in rainfall patterns or river flow régimes.

• High climate and weather variability, with floods and droughts, have been and might be normal for Namibia

8/18/2014

FLOODS AND DROUGHTS IN NAMIBIA

– No permanent rivers in interior – Main rivers on border and

flooding from higher rainfalls in headwaters in neighboring countries (Angola, Zambia)

– Highest population density in these areas

– Very high variability in river flows

• Between dry and wet season • Between successive years

FLOODS AND DROUGHTS IN NAMIBIA

DROUGHT

A period of abnormally dry weather long enough to cause a serious hydrological imbalance

Meteorological drought: a period with a (an abnormal) precipitation deficit

Agricultural drought: shortage of precipitation during the growing season that impinges on crop production or grazing conditions

Hydrological drought: shortage of precipitation during the runoff and recharge season that affects riverflows and water resources

FLOODS AND DROUGHTS IN NAMIBIA

• Battling with the devastating droughts 2013

FLOODS AND DROUGHTS IN NAMIBIA

Disaster: impact (loss of human lives, evacuations, direct damages, indirect losses, services disruptions, health risks, response, recovery, reconstruction)

FLOODS AND DROUGHTS IN NAMIBIA

FLOODS AND DROUGHTS IN NAMIBIA

• Namibia shares all its perennial rivers with neighboring countries

Mainly fed from high rainfall areas in headwaters of the riparian states

FLOODS AND DROUGHTS IN NAMIBIA

FLOOD FORECASTING AND EARLY WARNING Sources of information: • Weather and rainfall forecasts and observations:

– NMS, INAMET, ZMD, SAWS • Remote sensing/internet – eumetsat, NASA • Riverflows:

– Telemetry stations: satellite, cellular network – Local observers - NamWater – Hydrology teams – DWA Zambia, ZRA, DNA Angola, DWA Botswana, DWA South Africa – Remote sensing, EU-JRC, DFO-NASA

• Satellite images: – Space charter: 2008, 2009 (2x), 2011 – NASA, CSA, DLR, ESA, NSPO – Internet – MODIS

FLOODS AND DROUGHTS IN NAMIBIA

REAL-TIME RIVERFLOW INFORMATION

Flow level gauges Observers Telemetry Satellite transmission (‘HYCOS DCPs’)

Cellular network transmission (sms messages, GPRS)

FLOODS AND DROUGHTS IN NAMIBIA

FLOODS AND DROUGHTS IN NAMIBIA

RAINFALL MEASUREMENTS AND ESTIMATES

Ground stations: point measurements

Telemetry

Remote sensing: area estimates UNESCO-GWADI: 3-hour intervals (1-2 hour delay) NASA-Servir/TRMM: 3-hour intervals (6-hour delay) FEWS: daily intervals (2-day delay Eumetsat: 15-min intervals (real-time) RSMC/SWFDP: 1-hour intervals (near-real-time)

FLOODS AND DROUGHTS IN NAMIBIA

SATELLITE-BASED RAINFALL ESTIMATION Observe G-WADI http://hydis.eng.uci.edu/gwadi/ dex.htm satellite rainfall accumulation for the past 24 hours

UNESCO-GWADI G-WADI used for early warning and rainfall monitoring within the country and Transboundary

24 48 72 • 3 hours precipitation totals

(1-2 hours delay)

hours accumulative

rainfall

Namibia flood and drought

Rainfall accumulation for the past 24 hours ending at 08h54 am Using GWADI data

Bulletin +/- 600 recipients You can also view past and present daily flood bulletins and other flood information on Namibia at NASA's Namibia Flood Dashboard http://matsu.opencloudconsortium.org/namibiaflood

Challenges

• Climate variability and unpredictability • Real time data /monitoring upstream together

with real time communication- • Trasboundary nature of floods and droughts • Trasboundary data is almost inaccessible • Lack of in- situ rainfall measurement data • Human Resource capacity-skill shortage

Recommendations and Discussions

– UNESCO GWADI is a suitable tool for real time estimation of rainfall estimation at catchment level

– Satellite based approach is no real substitute for ground measurements, but it provides immediate indicative information for large areas

– Calibration and validation using ground observation data .

– Trans boundary information exchange, engage Riparian states?

Recommendations and Discussions

– Training on using and understanding of software physics

– Explore applicability of G-WADI satellite based rainfall estimation as inputs for flood forecasting modeling

– Explore applicability of G-WADI satellite based rainfall estimation at sub catchment level

– Explore drought early warning capabilities of the system at local level for communities

FLOODS AND DROUGHTS IN NAMIBIA