Potential Impacts of Hydrologic Uncertainty and Climate Change on Regional Power Options in the Lake Victoria Basin

Transcription

1 Potential Impacts of Hydrologic Uncertainty and Climate Change on Regional Power Options in the Lake Victoria Basin Johan Grijsen Hydrologist and WRM Specialist Bank Consultant Water Week WB March 1, 2007

2 Overview Historic hydrologic variability; Hydrology Debate Current hydrology with low lake Victoria levels due to over-abstraction for hydropower Agreed Curve releases of Lake Victoria Potential impacts of Climate Change (CCI) on hydrologic variability NVE study for Rusumo Falls catchment, 2006 SNC_L/Stratus study for LV Basin and power options, 2006 Consequences for power options in NEL Region

3 Equatorial Lakes and the Sudd/Bahr el Jebel

4 Lake Victoria Basin (Lake area 68,000 km 2; catchment area 190,000 km 2 )

5 1, , , , , , , ,133.0 Lake Victoria - Time Series of Water Level to 2005 Jan-00 Dec-04 Dec-09 Dec-14 Dec-19 Dec-24 Dec-29 Dec-34 Dec-39 Dec-44 Dec-49 Dec-54 Dec-59 Dec-64 Dec-69 Dec-74 Dec-79 Dec-84 Dec-89 Dec-94 Dec-99 Dec-04 The Hydrology Debate (what happened in the early 19-sixties?) Date Lake Level (m)

6 Lake Victoria: Variability of NBS and Lake Outflow Victoria Lake - Time Series of Net Basin Supply and Outflows to ,000 2,500 NBS and Outflow (m3/s) 2,000 1,500 1, Year NBS (m3/s) Outflow

7 Kagera river flows at Rusumo Falls ( )

8 Historical NBS Lakes Victoria, Kyoga and Albert

9 Historic Lake Victoria Levels (Nicholson and Tate et. al., 2001)

10 Rainfall Lake Victoria Basin ( : 1978: Lake Rainfall = 1,858 mm; Lake evaporation = 1,595 mm)

11 Mean annual run-off (WATBAL model) (Univ. of New Hampshire) Catchment area of Lake Victoria: 190,000 km 2 ; Tributary inflow Lake Victoria for : 1995: 26.5 BCM = 140 mm/yr Runoff-coefficient Lake Victoria Basin < 0.10

12 Lake Victoria Net Basin Supply (100 years average) A FRAGILE WATER BALANCE Tributary Inflow 15% Rainfall 85% Evaporation 80% Lake Victoria Abstraction 20% (power, water supply, etc.) Historic High in 1964: m Historic Low in 1920s: ~ m No-Flow Level ~ m Nalubaale/Kiira Dam *Note: Figures for any particular year may vary sharply from these long-term averages

13 Above (blue) and below-normal (red) SPI for LV basin (NOAA)

14 Annual releases at Jinja (in MCM/yr) vs. AC discharges Annual Water usage Annual Discharges Annual average Lake Levels Years 0 Agreed Curve annual discharge Actual discharge through Turbines Series5 Actual discharge Across Dam Annual average Lake Levels+Sheet3!$P:$P+Sheet3!$P:$P

15 Lake Victoria: levels and flows 09/ /2007

16 Agreed Curve release strategy for Lake Victoria Releases according to AC maintain hydrological and environmental integrity of Lakes Victoria, Kyoga and Albert, and of the Sudd wet lands A modified AC strategy would reduce releases below the AC in times of power surplus, for use above the AC in times of power shortage

17 Lake Victoria near Kisumu Kisumu (Oct. 2004) Jinja gauge level m

18 NEL Region s s Power Options (SNC-L L & Stratus CI, 2006) Proposed hydro- options in LV Basin (SSEA assessment) Nalubaale 180 MW (exist.) Kiira 208 MW (exist.) Bujagali 250 MW (2011) Rusumo 62 MW (2011) Kabu MW (2013) Ruzizi III 82 MW (2014) Ruhudji 358 MW (2015) Karuma 200 MW (2017) Rumakali 222 MW (2020) Murchison Falls 420 MW??

19 Expected CC impact on rainfall by 2100

20 Rusumo Falls catchment

21 Kagera river at Rusumo Catchment area 30,000 km 2 ; average rainfall 1,100 1,250 mm Runoff m 3 /s ( mm/yr) Runoff coefficient: 0.14 (pre-1961) to 0.21 (post-1961) Runoff coefficient Kagera river at entry Lake Victoria: 0.10

22 Simulated and observed flows for Rusumo Falls (NVE, 2006; HBV-model)

23 Climate change impact on annual average flows at Rusumo Falls Kagera river may (or may not) regress to its pre-1961 regime Annual flows may vary for extended times from 150 to 250 m 3 /s HEP design to be based on average flow of 200 m 3 /s (average 50 MW), high flow variability and small life storage (< 1 BCM) Climate change may increase rainfall with 5 10% and flows with 10 20% Design optimization of Rusumo Lake and installed capacity (60-75 MW?) to take hydrological variability/uncertainty into account.

24 Study area Climate Change Impact on Rainfall, Temp. and Runoff (Stratus CI, 2006 & (Stratus CI, 2006) Mean annual run-off for WATBAL calibration

25 Climate Change Analysis (Stratus CI, 2006) with projections for Uganda and Rwanda; A1B scenario Baseline ; projections of temperature and rainfall for 2050 and 2100,, for CC scenarios A1B 7 best performing GCMs for the region: CERG, CCSR, CSIRO, ECHAM3,, ECHAM4, HadCM2 and HADCM3 CO 2 sensitivity: 3 0 C

26 Sensitivity analysis for CCI on runoff and Annual average of CCI on runoff (Stratus CI, 2006) * runoff variability due to change in rainfall: multiplier * runoff reduction due to increase in temperature: 2 to 4% per degree 0 C

27 Potential impact CC on Lake Victoria s water balance in red: hydrology in blue: hypothetical dry year: with NBS = 40% of long-term average Rwanda and Uganda part of LV Basin: high probability of increased runoff Tanzania: high probability of increased seasonality in runoff low probability of rainfall reduction in the region Climate change may increase NBS for LV with at mm/yr, say 25 MCM/d = 50 MW at Nalubaale/Kiira power stations Generate multiple 100-years rainfall series, superimpose CCI, run series with Rainfall - Runoff models and assess optimal plant commissioning dates for Victoria Nile Parameter mm/year (in 2000) CC Impact (in %) mm/year (in 2050) Difference (in mm/yr) Rainfall 1,860 1, % + 10% 2,046 1, Evaporation -1,600-1, % + 4% -1,664-1, Tributary Inflow % + 15% Net Basin Supply % + 83%

28 Power development on Victoria Nile Lake Victoria Basin may (or may not) regress to its pre-1961 regime Annual releases may vary from MCM/d (pre-1961 and present) to MCM/d (1961 late nineties) Accordingly average power at Jinja (N/K) and Bujagali (2011) varies each from MW (2.1 Q), and at Karuma from MW (2.5 Q); Present demand: 100 MCM/d = 210 MW; >35% load shedding; Karuma needed < 2017 HEP design to be based on average flow of 75 MCM/d, high flow variability and Modified Agreed Curve (MAC) release strategy Climate change may increase rainfall in 2050 with 10%, inflows with 20% and NBS with MCM/d (50 MW each at N/K and Bujagali); Low firm power: advance commissioning of new plants, export temporary energy surpluses, adopt MAC strategy for saving lake waters at times of surplus, emergency thermal facilities.

29 Concluding remarks Hydrological versus political uncertainties Power demands in the NEL region are overwhelming Delays in commissioning of new plants caused by long preparation processes overshadow CCI on the short to medium term (early commissioning of Bujagali HEP would have prevented current low levels of LV) Focus on early implementation of Bujagali (2011) and Karuma (< 2017) on the Victoria Nile, to safeguard wetlands of Lake Victoria and the economy of Uganda For Rwanda and Burundi: early implementation of Rusumo HEP (2011) and Kabu 16 (2013) THANK YOU