4. Agricultural flood damage assessment in developing countries

The method for flood damage assessment for rice crops presented in this chapter was applied to assess agricultural damage in the river basins of developing countries in Asia. The method was verified by comparing calculated damage with reported data. In this section, the case studies of the assessment of flood damage to rice crops in the Pampanga River basin of the Philippines and the Lower Indus River basin of Pakistan are discussed.

#### 4.1 Pampanga River basin of the Philippines

The Pampanga River basin is located in the Region III of the Philippines, which is regarded as one of the most important river basins in terms of economic activities that influence the entire country. Figure 7 shows the location of the Pampanga River basin. It is the nation's fourth largest basin and covers an area of 10,434 km<sup>2</sup> . The main river is about 260 km long.

In the case of the Pampanga River basin, the results of flood damage assessment for the past largest flood event as well as for a 100-year flood case are discussed. To assess flood damage to rice crop in the Pampanga River basin of the Philippines, flood characteristics such as flood depth and duration were computed using the RRI model. A digital elevation model (DEM) of a 450 m 450 m grid size, derived from the Interferometric Synthetic Aperture Radar (IfSAR), was used in the RRI Model simulation. The IfSAR data was obtained from the National Mapping and Resource Information Authority (NAMRIA) of the Philippines. The flow accumulation and flow direction data, which are also necessary to input in the RRI model, were

created using DEM in ArcGIS. Hourly rainfall and water-level data were collected from the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA). The RRI model was calibrated and validated based on recent flood events by comparing the calculated and observed flood discharges at the San Isidro station in the basin. The flood event in September 2011 was the biggest flood in the basin in the last 30 years. The model parameters were thus calibrated to the September 2011 flood event. The calibrated parameters were validated with the 2015 flood event. Figure 8 shows the comparison of the calculated discharge with the observed discharge at San Isidro gauging station for the flood events in 2011 and 2015 and also the comparison of the calculated flood inundation depths with the recorded flood depth in the barangays (villages) of Calumpit Municipality. The calculated results reasonably agreed with the observed data. The flood event in 2011 was due to Typhoons Pedring and Quiel. Typhoon Pedring was directly followed by Typhoon Quiel, and rice crops were severely damaged by this flood event. The flood event in 2015 was due to Typhoon Lando, which also damaged rice-crop areas in the basin.

To calculate the flood inundation depth and duration for a specific return period, flood frequency analysis was conducted by using 48-hour maximum annual rainfall data. Flood frequency analysis is essential for calculating expected damage. The main objective of flood frequency analysis is to relate the magnitude of extreme events to their frequency of occurrence through the use of probability distributions [17, 18]. The Gumbel distribution method was used for rainfall analysis. Since the rainfall volume of the September 2011 flood during Typhoon Pedring was the highest rainfall volume in the last 30 years, the rainfall pattern of the September 2011 flood (only for the Typhoon Pedring case) was selected for designing a rainfall pattern for a specific return period. Figure 9 shows the results of flood frequency analysis using the Gumbel method and the estimation of a design hyetograph for an event of a specific return period such as a 100-year flood. To calculate flood characteristics for a 100-year flood, a design hyetograph for a 100-year return period was estimated by multiplying the rainfall hyetograph of the September 2011 flood by a conversion factor. The conversion factor for a 100-year return period was

method presented in Table 3. When flooding occurs during the early growth stage of rice plants, i.e., from the seedling to vegetative stages, at which no rice production is expected, farmers normally replant rice crops. In such a case, flood damage to rice crops can be estimated as losses of cost of input. On the other hand, when flooding occurs during the reproductive and maturity stages, at which rice production is usually expected, there is no time for replanting rice crops. In this case, flood damage to rice crops can be estimated as volume of production losses, i.e., yield loss, and then the value of production losses can be estimated based on farm gate price as calculation method presented in Table 3. The yield loss caused by flooding can be determined using a flood damage curve presented in Figure 6, according to flood

Calculation method of flood damage to rice crop for each growth stage of rice plants.

hectare yield loss

Reproductive stage (46–75 days) Volume of losses = most recent yield/hectare area damaged yield loss

farm gate price

Value of production losses = area affected cost of input/

Value of production losses = volume of losses most recent

Growth stage of rice Calculation method

Seedbed/seedling (20 days from rice plant

Recent Advances in Flood Risk Management

Newly planted stage (1–20 days after

Vegetative stage (21–45 days)

Maturing stage (76–115 days)

germination)

sowing)

Table 3.

4. Agricultural flood damage assessment in developing countries

The method for flood damage assessment for rice crops presented in this chapter was applied to assess agricultural damage in the river basins of developing countries in Asia. The method was verified by comparing calculated damage with reported data. In this section, the case studies of the assessment of flood damage to rice crops in the Pampanga River basin of the Philippines and the Lower Indus River basin of

The Pampanga River basin is located in the Region III of the Philippines, which is regarded as one of the most important river basins in terms of economic activities that influence the entire country. Figure 7 shows the location of the Pampanga River basin. It is the nation's fourth largest basin and covers an area of 10,434 km<sup>2</sup>

In the case of the Pampanga River basin, the results of flood damage assessment for the past largest flood event as well as for a 100-year flood case are discussed. To assess flood damage to rice crop in the Pampanga River basin of the Philippines, flood characteristics such as flood depth and duration were computed using the RRI model. A digital elevation model (DEM) of a 450 m 450 m grid size, derived from the Interferometric Synthetic Aperture Radar (IfSAR), was used in the RRI Model simulation. The IfSAR data was obtained from the National Mapping and Resource Information Authority (NAMRIA) of the Philippines. The flow accumulation and flow direction data, which are also necessary to input in the RRI model, were

.

depth and duration.

Pakistan are discussed.

118

4.1 Pampanga River basin of the Philippines

The main river is about 260 km long.

Comparison of calculated discharge with observed discharge at San Isidro station (a), (b) and comparison of calculated flood depth with recorded depth at each barangay (village) of Calumpit municipality (c).

wet-season rice cultivation in the Pampanga River basin. The cropping calendar is based on the cropping calendar prepared by the National Irrigation Administration-Upper Pampanga River Integrated Irrigation System. The wet-season rice cultivation period in the Pampanga River basin is from June to October, and at least one flood event occurs every year during this period due to heavy rainfall or typhoons. Flood damage was assessed for the 2011 flood event and 100-year flood cases. Based on the duration of the growing stage of rice crop and the cropping calendar (Figure 5 and Figure 10(b)), the growth stage of rice crop during the flood event in 2011 was the maturity stage. The flood damage curves for the maturity stage presented in Figure 6 were thus employed to estimate rice-crop damage. The ricecrop damage for a 100-year flood was estimated based on the current conditions, assuming that the rice plants were at the maturity stage, similar to the stage of rice crop during the past flood case. The flood damage to rice crop was estimated as volume of production losses using the calculation method presented in Table 3. Figure 11 shows the calculated flood hazard areas and agricultural damage during the flood event from 26 September to 4 October 2011 caused by Typhoons Pedring and Quiel. The estimated flood inundation areas with a flood inundation depth greater than 0.5 m were 101,736 ha. The estimates of damaged rice-field area and rice-crop damage were 45,056 ha and 1475.78 million peso, respectively. The values of the farm gate price equal to 17 peso/kg [14] and the rice yield equal to 4360 kg/ha

Paddy field and cropping calendar for wet-season rice crop in the Pampanga River basin.

Methodology for Agricultural Flood Damage Assessment DOI: http://dx.doi.org/10.5772/intechopen.81011

Figure 10.

121

#### Figure 9.

Flood frequency analysis and estimation of the design hyetograph for an event of a specific return period such as 100-year flood.

calculated as the ratio of the corresponding rainfall of the return period and the 48 hour maximum annual rainfall of 2011 based on a frequency curve. The return period of the September 2011 flood event was about 28 years. The flood characteristics for a 100-year flood were simulated by using the RRI model and the calculated design hyetograph.

Figure 10(a) shows the paddy fields in the Pampanga River basin, extracted using a land-cover map prepared by NWRB and JICA [12]. The rice-crop areas in the basin are about 397,247 ha. The paddy fields account for about 38% of the basin area in the Pampanga River basin. Figure 10(b) shows the cropping calendar for the Methodology for Agricultural Flood Damage Assessment DOI: http://dx.doi.org/10.5772/intechopen.81011

#### Figure 10.

Paddy field and cropping calendar for wet-season rice crop in the Pampanga River basin.

wet-season rice cultivation in the Pampanga River basin. The cropping calendar is based on the cropping calendar prepared by the National Irrigation Administration-Upper Pampanga River Integrated Irrigation System. The wet-season rice cultivation period in the Pampanga River basin is from June to October, and at least one flood event occurs every year during this period due to heavy rainfall or typhoons.

Flood damage was assessed for the 2011 flood event and 100-year flood cases. Based on the duration of the growing stage of rice crop and the cropping calendar (Figure 5 and Figure 10(b)), the growth stage of rice crop during the flood event in 2011 was the maturity stage. The flood damage curves for the maturity stage presented in Figure 6 were thus employed to estimate rice-crop damage. The ricecrop damage for a 100-year flood was estimated based on the current conditions, assuming that the rice plants were at the maturity stage, similar to the stage of rice crop during the past flood case. The flood damage to rice crop was estimated as volume of production losses using the calculation method presented in Table 3. Figure 11 shows the calculated flood hazard areas and agricultural damage during the flood event from 26 September to 4 October 2011 caused by Typhoons Pedring and Quiel. The estimated flood inundation areas with a flood inundation depth greater than 0.5 m were 101,736 ha. The estimates of damaged rice-field area and rice-crop damage were 45,056 ha and 1475.78 million peso, respectively. The values of the farm gate price equal to 17 peso/kg [14] and the rice yield equal to 4360 kg/ha

calculated as the ratio of the corresponding rainfall of the return period and the 48 hour maximum annual rainfall of 2011 based on a frequency curve. The return period of the September 2011 flood event was about 28 years. The flood characteristics for a 100-year flood were simulated by using the RRI model and the calculated

Flood frequency analysis and estimation of the design hyetograph for an event of a specific return period such as

Comparison of calculated discharge with observed discharge at San Isidro station (a), (b) and comparison of calculated flood depth with recorded depth at each barangay (village) of Calumpit municipality (c).

Figure 10(a) shows the paddy fields in the Pampanga River basin, extracted using a land-cover map prepared by NWRB and JICA [12]. The rice-crop areas in the basin are about 397,247 ha. The paddy fields account for about 38% of the basin area in the Pampanga River basin. Figure 10(b) shows the cropping calendar for the

design hyetograph.

Figure 9.

120

100-year flood.

Figure 8.

Recent Advances in Flood Risk Management

#### Figure 11.

Calculated maximum flood inundation depth using the RRI model and estimated flood damage to rice crop by the flood event from 26 September to 4 October 2011.

pesos, respectively. In this case, the rainfall pattern and period of Typhoon Pedring were exclusively considered for designing a rainfall hyetograph for a 100-year flood. If the rainfall pattern and period of Typhoons Pedring and Quiel are considered, the damage might be more severe. The estimated value of rice crop in the case

Figure 14 shows the location of the Lower Indus River basin in Pakistan. The

GLCNMO were used to extract paddy fields, and Figure 15(a) shows the paddy

. The global land-cover data of

of a 100-year flood is about 1.52 times as high as that in the 2011 flood case. Identifying flood risk areas based on flood damage assessment provides essential information for designing future development activities. The results of flood hazard and damage assessment can be useful for implementing mitigation actions as well as for formulating policies for flood risk reduction including land-use management. To evaluate the risk of a flood with a specific return period, target scales for risk assessment should be determined. Basically, such target scales are decided based on the socioeconomic conditions of target areas and consensus among stakeholders

Calculated flood inundation depth and rice-crop damage for a 100-year flood case.

Methodology for Agricultural Flood Damage Assessment DOI: http://dx.doi.org/10.5772/intechopen.81011

such as national and local governments.

Figure 13.

Figure 14.

123

4.2 Lower Indus River basin of Pakistan

area of the study basin is about 700,375 km2

Study area of the lower Indus River basin in Pakistan.

#### Figure 12.

Comparison of calculated value of rice-crop damage with reported data for five municipalities during the flood from 26 September to 4 October 2011. Reported data source: [19, 20].

[19] were used in the calculation. About 11.3% of the total paddy-field area in the basin was damaged during this flood event. Figure 12 compares the calculated ricecrop damage with the reported data for five municipalities in the basin. The calculated results reasonably agreed with the reported damage, although some difference was found in the case of Candaba Municipality. This discrepancy between the calculated and reported damage can be attributed to a variety of reasons, for example, accuracy of topographical and land-cover data.

Figure 13 shows the calculated maximum flood inundation depth and flood damage to rice crop for a 100-year flood. The damaged paddy fields and value of rice-crop damage in the case of a 100-year flood were 67,655 ha and 2248.3 million Methodology for Agricultural Flood Damage Assessment DOI: http://dx.doi.org/10.5772/intechopen.81011

#### Figure 13.

Calculated flood inundation depth and rice-crop damage for a 100-year flood case.

pesos, respectively. In this case, the rainfall pattern and period of Typhoon Pedring were exclusively considered for designing a rainfall hyetograph for a 100-year flood. If the rainfall pattern and period of Typhoons Pedring and Quiel are considered, the damage might be more severe. The estimated value of rice crop in the case of a 100-year flood is about 1.52 times as high as that in the 2011 flood case. Identifying flood risk areas based on flood damage assessment provides essential information for designing future development activities. The results of flood hazard and damage assessment can be useful for implementing mitigation actions as well as for formulating policies for flood risk reduction including land-use management. To evaluate the risk of a flood with a specific return period, target scales for risk assessment should be determined. Basically, such target scales are decided based on the socioeconomic conditions of target areas and consensus among stakeholders such as national and local governments.
