Field Surveys

The results of the first survey showed the need for weather and climate forecasting mainly at critical points of the rice growing seasons: the onset of the rainy season, the occurrence of dry spells during the rainy season, the salinity conditions at the end of

01 234567801 2345678 Lag time (months! Lag time (months)

Fig. 18.2. Correlation coefficients between Niño 3.4 SSTA (left) and SOI (right) with temperature (above) and rainfall (below), averaged for the MRD. Y-axis denotes calendar months from January (1) through December (12), x-axis denotes lag time in month

01 234567801 2345678 Lag time (months! Lag time (months)

Fig. 18.2. Correlation coefficients between Niño 3.4 SSTA (left) and SOI (right) with temperature (above) and rainfall (below), averaged for the MRD. Y-axis denotes calendar months from January (1) through December (12), x-axis denotes lag time in month the dry season and beginning of the rainy season and flood and inundation events. The lead-time required is one and three months in supplementation to the existing 10-day outlooks issued regularly by the Southern Regional HydroMet Center, SRHMC (located in Ho Chi Minh City). In addition, farmers expressed their desire to have the forecast of hydrological conditions in the forecasting bulletins. This is quite common here as their agricultural practices are affected very much by flow regime. The findings from the survey helped design suitable hydrometeorological forecasts, which include both climate outlook (for 1 month and 3 months) and hydrological conditions forecasts (for water level and salinity of several stations in the areas).

The results of the second survey showed that the climate forecasts based upon the results of the first survey were extremely useful for both farmers and agricultural workers. Farmers used the rainfall forecasts for defining the sowing dates and the harvest time. The three-month forecasts are very important for extension workers in guiding and defining farming schedules for local areas. The forecasts were used in farming arrangement, including time for sowing, fertilizer spraying, irrigation and selection of storage methods.

Forecast Information for Dissemination to Farmers

The communication between the forecasting centers and end users is shown in Fig. 18.3.

The forecasts were firstly made at the Regional Forecasting Center (RFC) located in Ho Chi Minh City. Then forecasts were sent to Long An Provincial Forecasting Center (LA PFC). The latter was responsible to finalize the bulletin and distribute the forecasts to related agencies and farmers in the province after adjusting the forecasts based on local conditions and requirements. This is the first time probabilistic forecasts were introduced to farmers. The possibilities and limitations of the seasonal forecasts were explained during meetings; however it was indicated that the users would prefer deterministic forecasts.

Crop Simulation

CERES-Rice model of DSSAT V3.5 software was used to simulate crop yield in Ben Luc and Tan Thanh districts (Long An province). In practice, different planting dates are applied at the locations, so the simulation was adjusted to reflect those planting dates.

Fig. 18.3. Communication of forecasts between forecasting centers and users

Fig. 18.3. Communication of forecasts between forecasting centers and users

Fig. 18.4. Simulated yields vs. observed yields at different planting dates The simulation was made with the actual weather data and crop inputs of the summer-autumn rice crop in 2003

The simulation results allowed us to define the optimum planting dates for the selected locations. For Tan Thanh district, the optimum planting date is around the first 10 days of April. For Ben Luc district, the optimum planting date is the first 10 days of May (Fig. 18.4). If planting occurred earlier or later than these planting dates, there is a possibility that a considerable decrease of the yield due to the water situation (shortage at the beginning or inundation at the end of growing period) may result.

The implementation of the project has established close cooperation between climate researchers, hydrometeorological operational forecasters in the regional and provincial levels, agricultural staff from Long An Department of Agriculture and Rural Development and staff from Long An Agricultural Extension Center. The project activities relating to rice production in the areas have received an enthusiastic involvement of local people (extension workers and farmers of Long An province).

18.4

Conclusions

Although the project has made some achievements, there are still some aspects that need to be considered and improved. They are as follows:

■ The forecast accuracy, especially in the longer term needs to be improved. It is suggested that further studies on the relationship between ENSO phenomena and climate variables over the Mekong River Delta be undertaken in more detail so that the findings can be used to assist operational forecasting work.

■ Improve forecast-distribution procedures of operational agencies to provide the best possible benefits of climate information for users.

In order to exploit the full benefits of the research results it is proposed to conduct a study on the effects of ENSO and climate change on water resources and the coastal zone of the Mekong River Delta.

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