Rice-Crops Flood Damage Assessment in the Pampanga River Basin of the Philippines 1*
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Badri Bhakta SHRESTHA , Hisaya SAWANO , Miho OHARA and Naoko NAGUMO 1International
Centre for Water Hazard and Risk Management (ICHARM), Public Works Research Institute (PWRI), Tsukuba, Japan *Correspondence:
[email protected]
1. Introduction
The rice crops damage curves as a function of flood depth and duration were developed based on linear interpolation of flood damage matrix data shown in Table 1 and by considering plant height of rice crops.
Risk of flood disaster has been increasing tremendously by rapid urbanization and development activities constituting threat to economies, population and sustainable development, which will be increased more by climate change impact. To reduce the risk of flood damage, risk assessment to identify existing risk in the areas is very essential. In this study, agriculture damage estimation method was developed for risk assessment and damage assessment was conducted in the Pampanga river basin of the Philippines. Agriculture damage refers here as damage occurring to rice-crops. The agriculture damage was defined as function of flood depth, flood duration and growing stage of crops. The calculated damages were compared with reported values.
The rice crops damages can be estimated by following equations: Loss Volume = Rice Yield x Damaged Area x Yield Loss
2. Study Area
In case of the Pampanga river basin, the values of farm gate price equal to 17 Peso/kg (BAS, 2013) and rice yield equal to 4,360 kg/ha (BPAO, 2011) were used.
The Pampanga river basin is the fourth largest basin in the Philippines and covers an approximate aggregate area of 10,434 km2. The total length of the main river is about 260 km. This river basin has two multipurpose dams i.e., Pantabangan (storage capacity of 2,966 million m3) and Angat (storage capacity of 850 million m3). There are two swamp areas Candaba (250 km2) and San Antonio (120 km2) in the river basin.
Pantabanga Dam
Fishpond 4.7% Swamp 0.5% Settlement 0.7% Built-up area 2.6%
Other cultivated area 6.8%
Water body 1.4%
Others (Natural) 2.8%
Others (Artificial) 0.2%
Production Loss Value = Loss Volume x Farm Gate Price
Fig. 6 Developed flood damage curves for rice crops
4. Results Figure 7 shows the calculated agricultural damage in the Pampanga river basin for September 2011 flood event. According to cropping calendar published by National Irrigation Administration, Upper Pampanga River Integrated Irrigation Systems (NIA-UPRIIS) in 2013, the stage of rice crops during September 2011 flood period is maturity stage. Thus, the damage functions of maturity stage were used to estimate the production loss of rice crops for September 2011 flood event. Table 2 Calculated and reported rice crops damages for September 2011 flood event
Forest 18.0%
Rice crops damages (million Peso) Brush land 24.3%
Paddy field 38.1%
Descriptions
Reported values
San Antonio Swamp
Calculated using proposed damage functions
Source: JICA IWRM Report Candaba Swamp
Angat Dam
Fig. 1 Location of study area Catchment Area: 10,434 km2 River Length: 260 km Average annual rainfall: 2155mm/year Population: 6.3 million Population Density: 460 persons / km2
Fig. 2 Land cover map Fisheries 8.2%, 985.943
Livestock 1.5%, 183.284 High-value Commercial Crops 7.8%, 940.243
Fig. 3 Percentage of agriculture damage in 24-28 September 2011 and estimated damage cost in million Pesos (in Region III)
Corn 0.2%, 21.118
Rice 82.3%, 9886.565
Source: Office of Civil Defense, Region III
3. Methodology
Pampanga River Basin (Affected area 45,900 ha)
-
1,461
Pampanga Province (Affected area 15,900 ha)
1,376
652
Calumpit Municipality (Affected area 1,250 ha)
37
42
Data Source for reported value: Office of Civil Defense, Region III
Pampanga Province
Calumpit Municipality
Fig. 7 Calculated agricultural damages for September 2011 flood event (500m x 500m grid) (a)
In Pampanga Province, the reported value of ricecrop damage also includes rice-crop damage due to strong winds in the area; thus, there is a difference between the calculated and reported rice-crop damage values in Pampanga Province. The flood event of September 2011 was caused by Typhoon “Pedring” and rice-crop damage occurred due to strong winds during the event. (b)
The grid-based distributed flood damage assessment method was developed to estimate the agriculture damages (Fig. 4). The hazard assessment for the damage estimation was conducted by using hydrological model. Rainfall Runoff Inundation (RRI) model developed by Sayama et al. (2012) was used to calculate the flood depth and duration and flood-prone areas were identified. The digital elevation model of HydroSHEDS which obtained from the Shuttle Radar Topography Mission (SRTM) data (15 arc-seconds grid size, approximately 500m x 500m grid size) was used in the study. The flood inundation depth and duration were calculated at 500 m x 500 m grid cell. The hourly rainfall and water level data were collected from the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA). RRI Model
Flood depth and flood duration
• • •
Topography Land use information Flow accumulation and direction data
Socio-Economic statistical data, Past flood information/damages
Damage functions
Land cover data -
Development of relationships between hazards and potential damages
Table 1 Flood damage matrix for rice crops Growth stage Vegetative stage: Minimum Tillering /Maximum Tillering Reproductive Stage: Panicle Initiation/Booting Stage (Partially Inundated) Reproductive Stage: Panicle Initiation/Booting Stage (Completely Inundated) Maturity Stage: Flowering stage Ripening Stage
Days of submerge 1-2 3-4 5-6 7 Estimated yield loss (%) 10-20 20-30 30-50 50-100 10-20
30-50
40-85
50-100
15-30
40-70
40-85
50-100
15-30 5
40-70 10-20
50-90 15-30
60-100 15-30
Source: BAS (2013)
Potential Flood Damage Assessment
Flood Risk Assessment
100
40
0
95 65 Days from seeding to harvest
40
Duration (days)
20
Growth Stage
Seedbed / Seedling
20 Newly Planted
25 Vegetative Stage
135
Flowering
Maximum tillering and panicle formation
20
Seeding
The agriculture damage function varies with its stages. Table 1 shows the ranges of rice crops damage due to floods for different stages of crops published by the Philippines Bureau of Agricultural Statistics (BAS, 2013). Figure 5 shows the days and plant height of rice crops at each growing stages.
Plant Height (cm)
Fig. 4 Overview of methodology
130
30 Reproductive Stage
Harvest
HydroMeteorological Data
40 Maturity Stage
Fig. 5 Days and plant height of rice crops at its each growing stage
Estimated Damages: 1,777.88 million pesos
Estimated Damages: 2,888.508 million pesos
Fig. 8 Estimated agricultural damages for (a) 50 Years return period and (b) 100 Years return period flood event (500m x 500m grid)
5. Conclusions For flood risk assessment, data on past flood hazards and past flood damage with their relationships are very important for development of an appropriate method for the basin as well as for validation of the calculated results. In the Pampanga river basin, the estimated affected area and value of rice crops damages in September 2011 flood event case were found to be 45,900 ha and 1,461 million Pesos, respectively. The estimated amount of agriculture damages for 50 and 100 years return period flood events were found to be 1,777.88 and 2,888.508 million pesos, respectively. Results from flood damage assessment can be useful for planners, developers, policy makers and decision makers to establish policies required for flood damage reduction. Reference 1. Bulacan Provincial Agricultural Office (BPAO), 2011: “Final validation report for cereals” BPAO, Philippines. 2. Bureau of Agricultural Statistics (BAS), 2013: “Manual on damage assessment and reporting system” Department of Agriculture, Philippines. 3. Sayama T., Ozawa G., Kawakami T., Nabesaka S. and Fukami K., 2012: “Rainfall-Runoff-Inundation analysis of Pakistan flood 2010 at the Kabul river basin” Hydrological Sciences Journal 57:2, 298-312.
