How Local People Use Their Indigenous Knowledge to Respond to Floods and Droughts: A Case Study of Tonle Sap Lake Community, Cambodia

<p>This thesis investigates the impacts of floods and droughts in the Tonle Sap Lake region and examines to what extent the local communities’ indigenous knowledge (IK) is used to deal with floods and droughts. The thesis begins by exploring the Tonle Sap Lake communities’ perceptions of climate change, especially floods and droughts and their impacts on local livelihoods. It then examines how the communities have used their IK to develop livelihood adaptation methods to cope with floods and droughts. To conduct this study, a qualitative methodology was adopted using semi-structured interviews, and non-participant and unstructured observation as the main methods. The semi-structured interviews were conducted with local people and local authorities from two communities, and NGO staff. The study found that the intensity of floods and droughts in the Tonle Sap Lake region has increased in the last few years. Floods and droughts have threatened local livelihoods and food security. To mitigate the effects of floods and droughts, the local communities in this region have developed various livelihood adaptation strategies to adapt to the hazards. The communities appeared to use both IK and technologies for their adaptation strategies. IK is seen as an invaluable local community asset in developing livelihood adaptation methods. Although a mixture of IK and new knowledge has been used to develop various adaptation strategies, the sufficiency of the adaptation is still limited. The current severity of climate change is seen to limit the local communities’ response capacities. To strengthen the communities’ adaptation capacity, contribution and involvement from non-governmental organisations and the government in developing climate change adaptation policy at a local level are essential.</p>

How Local People Use Their Indigenous Knowledge to Respond to Floods and Droughts: A Case Study of Tonle Sap Lake Community, Cambodia

<p>This thesis investigates the impacts of floods and droughts in the Tonle Sap Lake region and examines to what extent the local communities’ indigenous knowledge (IK) is used to deal with floods and droughts. The thesis begins by exploring the Tonle Sap Lake communities’ perceptions of climate change, especially floods and droughts and their impacts on local livelihoods. It then examines how the communities have used their IK to develop livelihood adaptation methods to cope with floods and droughts. To conduct this study, a qualitative methodology was adopted using semi-structured interviews, and non-participant and unstructured observation as the main methods. The semi-structured interviews were conducted with local people and local authorities from two communities, and NGO staff. The study found that the intensity of floods and droughts in the Tonle Sap Lake region has increased in the last few years. Floods and droughts have threatened local livelihoods and food security. To mitigate the effects of floods and droughts, the local communities in this region have developed various livelihood adaptation strategies to adapt to the hazards. The communities appeared to use both IK and technologies for their adaptation strategies. IK is seen as an invaluable local community asset in developing livelihood adaptation methods. Although a mixture of IK and new knowledge has been used to develop various adaptation strategies, the sufficiency of the adaptation is still limited. The current severity of climate change is seen to limit the local communities’ response capacities. To strengthen the communities’ adaptation capacity, contribution and involvement from non-governmental organisations and the government in developing climate change adaptation policy at a local level are essential.</p>

Characteristics of the Annual Maximum and Minimum Water Temperatures in Tonle Sap Lake, Cambodia from 2000 to 2019

The Tonle Sap Lake contains unique hydrological environments and ecosystems. Although water temperature is an important consideration in lake management, information on the water temperature of the lake is limited. Thus, we investigated the characteristics of the daytime water temperatures of the Tonle Sap Lake from 2000 to 2019 using MOD11A1, a Moderate Resolution Imaging Spectroradiometers (MODIS) product. Moreover, the relationship between water temperature fluctuations and hydrological–meteorological conditions was analyzed. The maximum and minimum daytime water temperatures were recorded in May (30.7 °C) and January (24.6 °C), respectively, each a month after the maximum and minimum air temperatures were recorded. The annual maximum, average, and minimum water levels showed a downward trend (−0.14, −0.08, and −0.01 m/y, respectively). The annual maximum water temperature increased at a rate of 0.17 °C/decade, whereas the annual minimum water temperature decreased at a rate of 0.91 °C/decade. The annual maximum daytime water temperature had a strong negative correlation with water level change (flood pulse) and a weaker correlation with air temperature. The annual minimum daytime water temperature presented the strongest positive correlation with water level change (flood pulse) in the previous year. However, there was no correlation between the annual minimum daytime water temperature and air temperature. These results indicate that water temperature in the Tonle Sap Lake is mainly affected by water level fluctuations, which are mainly driven by flood pulses.

Drastic decline of floodpulse in the Cambodian floodplains (the Mekong River and the Tonle Sap system)

The Cambodian floodplains experience a yearly floodpulse that is essential to sustain fisheries and the agricultural calendar. Sixty years of data from 1960–2019 are used to track the changes to the floodpulse there. We find that minimum water levels in 2010–2019 have increased by up to 1.55 m at Kratie and maximum water levels have decreased by up to 0.79 m at Prek Kdam when compared to 1960–1991 levels, causing a reduction of the annual flood extent. Concurrently, the duration of the flooding season has decreased by about 26 days (Kompong Cham) – 40 days (Chaktomuk), with the season starting later and ending much earlier. Along the Tonle Sap River, the average annual reverse flow from the Mekong to the Tonle Sap Lake has decreased by 56.5 %, from 48.7 km3 in 1962–1972 to 31.7 km3 in 2010–2018. As a result, wet-season water levels at Tonle Sap Lake has dropped by 1.05 m in 2010–2019 since 1996–2009, corresponding to a 20.6 % shrinkage of the Lake area. In addition to known upstream contributors such as hydropower dams, two anthropogenic causes of the drastic alterations to the floodpulse are identified: irrigation and channel incision. We estimate that water withdrawal in the Cambodian floodplains is occurring at a rate of (2.1 ± 0.3) km3/yr and incision-induced water levels reduction is in the order of (0.43–1.02) m. As the floodpulse is essential for the ecological habitats, fisheries and livelihoods of the region, its reduction will pose major implications throughout the basin, from the Tonle Sap system to the Vietnamese Mekong Delta downstream.

Impact of Wind on the Spatio-Temporal Variation in Concentration of Suspended Solids in Tonle Sap Lake, Cambodia

Even though wind, water depth, and shear stress are important factors governing sediment resuspension in lakes, their actual relations to total suspended solids (TSS) distribution in natural environments have not been well elucidated. This study aims to elucidate the impact of the wind on the spatio-temporal variation of TSS in Tonle Sap Lake, Cambodia, during low-water (March and June, <1 m) and high-water (September and December, 8–10 m) seasons. To this end, wind and TSS data for December 2016 and March, June, and September 2017 were collected and analyzed. For spatial interpolation of wind speed, the inverse distance weighted method was found to be better (R2 = 0.49) than the vectorized average (R2 = 0.30) and inverse of the ratio of distance (R2 = 0.31). Spatial interpolation showed that the wind speed and direction on the lake were <5 m/s and southward during the low-water season and <7 m/s and westward during the high-water season. The TSS concentration in the low-water season was higher (>50 mg/L) than that in the high-water season. The TSS concentration during the low-water season was empirically described by wind speed (W), water depth (D), and shear stress (τ_wave) with a function of W3, W3/D, and exp(W/D) or exp(τ_wave), depending on the location in the lake. The critical shear stress due to wind-induced waves at most of the places in the lake was higher than the total shear stress indicated. Sedimentation was predominant in December and June, and erosion (siltation) was dominant in March. Most of the siltation in March was dominant in the southern part of the lake.

Multiyear analysis of the dependency of the planting date on rainfall and soil moisture in paddy fields in Cambodia, 2003–2019

The dependencies of the planting date on rainfall and soil moisture in paddy fields in Cambodia were analyzed to quantify farmers’ empirical knowledge regarding their decision of the planting date. Remote sensing data from multiple satellites covering the 2003–2019 period were analyzed. The planting dates in rain-fed paddies ranged from April to August, with large spatial variations and year-to-year fluctuations. In years when planting was suppressed in April and May, planting was extensively enhanced in June and August compared to normal years, and vice versa. Over the northeastern side of Tonle Sap Lake and south of Phnom Penh city, the areas planted in April and May were found to have positive correlations with rainfall and soil moisture, suggesting that wetter-than-average conditions encouraged farmers to plant earlier in the season. In contrast, this relationship was unclear on the western side of Tonle Sap Lake, where the rainfall amounts were larger throughout the year than in other areas in Cambodia. In this region, the relationship between the planting area and soil water availability was either unclear or was even slightly negative from June to August. Since more frequent dry spells have been detected after the onset of the rainy season in recent years, further studies and disseminations of potential changes in dry spells are important for the agronomic adaptation of planting dates under climate change.