The Tonle Sap Lake plays a key role in the livelihoods of the people of Cambodia,
accounting for about 60% of Cambodia’s inland fisheries production (Baran et al. 2007). The hydrology of the lake is closely linked to the productivity of capture fisheries, so any potential changes under climate change could have significant impacts on the Cambodian population.
The dynamics of both the area flooded and the water levels in the lake are important for the productivity of capture fisheries, so relationships between modelled lake storage volumes and flooded area (Figure 7.1) and water level (Figure 7.2) were used to estimate lake area and water levels under historic and projected climate conditions. The remote sensing techniques and methodology used to derive the relationship between Tonle Sap modelled storage volumes and lake area are described fully in Appendix 2.
y = 0.1426x - 825.14 R2 = 0.8073
0 2000 4000 6000 8000 10000 12000 14000 16000 18000
20000 40000 60000 80000 100000 120000
Tonle Sap modelled storage (mcm)
TRMM scaled and MODIS flood extent (km2)
Figure 7.1. Scatterplot of the combined MODIS (2000-2002) and scaled TRMM (1998- 2002) monthly flood extent for the Tonle Sap Lake verses modelled monthly water volume.
Under the most likely projections for 2030, storages in the lake will increase causing both the maximum and minimum area of the lake to increase each year (Figure 7.3). The size of projected increases in maximum area shown in Figure 7.3 is intended to be indicative only.
The linear relationship between Tonle Sap storage and area used to estimate the area of the lake was derived using images with a maximum area of flooding of ~15,000 km2 (Figure 7.2).
There is uncertainty associated with extrapolation of this relationship to greater storages and areas. The maximum area of the lake during the wet season is projected to increase by an average of 3600 km2. During the dry season, the edge of the lake is projected to expand by an average of 165 km2 (Figure 7.3).
y = 9E-05x - 0.7368 R2 = 0.9884
0 2 4 6 8
0 10000 20000 30000 40000 50000 60000 70000 80000 90000 Tonle Sap Storage (mcm)
Water level (m)
Figure 7.2. Relationship between modelled water volume in the Tonle Sap lake, and water levels in the lake derived from Baran et al. 2007.
Under the most likely projections for 2030 the maximum and minimum levels of the Tonle Sap Lake will also increase (Figure 7.4). Minimum levels are projected to increase by an average of 0.1 m, and maximum levels by an average of ~2.3 m each year.
The net impact of the projected increase in both maximum and minimum area is likely to be complex, with potential for both positive and negative effects. Greater flood volumes have been associated with an increase in capture fisheries from the lake, but there may be negative impacts associated with damage to agricultural areas, housing and infrastructure.
Because of the likely increase in minimum area of the lake, some of the flooded forest within this area will become permanently submerged and is likely to be destroyed. The forest acts as a buffer protecting the floodplain against erosion under stormy conditions. It also provides habitat which is important as a fish breeding, feeding and shelter area (Baran et al. 2007).
Increased runoff from the Tonle Sap catchment and upstream catchments of the Mekong is likely to increase input of sediments, influencing nutrient cycling in the lake and the fertility of cropping enterprises on the floodplain. The survival rate of fish eggs may be affected
through the interaction of egg buoyancy and sediment load. Flows to and from the Mekong River will increase, and changes in flow may influence the drift of eggs, larvae and juveniles.
The timing of the onset of flood is also likely to be impacted, with water levels rising earlier in the year, and the duration of the flood each year likely to increase (Figure 7.5). Clearly, the impacts of climate change on the complex ecology of the floodplain are diverse and inter- related, and require further investigation to elucidate them and determine the flow on effects on the population, livelihoods and the economy of the region.
2000 2500 3000 3500 4000
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Area (km2 )
historic climate
2030 climate (median) minimum
5000 10000 15000 20000 25000
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Area (km2 )
historic climate
2030 climate (median) maximum
Figure 7.3. Historical (1951-2000) and future (2030) maximum and minimum area of Tonle Sap Lake
minimum
1.0 1.5 2.0 2.5
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
water level (m)
Historical climate 2030 climate (median)
maximum
4 8 12 16
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
water level (m)
Historical climate 2030 climate (median)
Figure 7.4. Historical (1951-2000) and future (2030) maximum and minimum annual water level of Tonle Sap Lake.
0 5,000 10,000 15,000 20,000 25,000
May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr
Tonle Sap Area (km2 )
2030 climate range 2030 climate (median)
Historical climate
0 3 6 9 12 15
May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr
Tonle Sap Water Level (m)
2030 climate range 2030 climate (median)
Historical climate
Figure 7.5. Historical (1951-2000) and future (2030) seasonal fluctuation in area and water level of Tonle Sap Lake.
8. IMPACT OF CLIMATE CHANGE ON AGRICULTURAL