A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Disaster Preparedness, Mitigation and Management, School of Environment, Resources and Development

Thesis (M. Eng.) - Asian Institute of Technology, 2010

Drought is a natural hazard considered to be part of the climate. This study focused on two main parts which are thorough analysis of available hydro-meteorological data and drought risk assessment and management in Cagayan and Isabela Provinces in the Philippines. The climate trend was analyzed using Hilbert Huang Transform which was developed to analyze erratic sets of data. The trend posted slightly increasing precipitation, decreasing minimum atmospheric temperature except for Echague. The maximum temperature, however, is decreasing inland but there is an increasing trend in the coast. RH has fairly the same trend outcome from different stations. Monthly based observation gives a varying trend as well. Aparri and Tuguegarao give a consistent trend in all months especially on the minimum and maximum atmospheric temperature as well as relative humidity. Additionally, the future trends of daily hydro-meteorological data was also analyzed and projected for the next 10 years utilizing the trend results from 1999-2008. The present and projected results which were in year 2008 and 2018 respectively were utilized in order to analyze the effect of changes in the climate on rice production using the data of the different weather stations as scenarios. Result shows increase in rice production from 2008 to 2018 in both irrigated and rainfed rice plantation areas. Drought risk was assessed initially by identifying drought occurrences through meteorological indices such as SPI and PDSI. Aparri SPI 1 (SPI = -3.37) has the lowest value for extremely dry condition among the minimum extreme values of the 4 SPI time scales, however, it has the shortest duration. Tuguegarao SPI 3 gives the lowest value (SPI = -3.48); which has a duration of 8 months considering the near normal values in between. PDSI results in Aparri, has the lowest value at PDSI = -5.02, lasted for 3 years and 7 months. Tuguegarao indicated a PDSI value of -5.41 which is within a drought period of 14 months which started from October 1963. Meteorological drought occurrences are also evident in the last 10 years. Agricultural drought in this study was identified using SMI which is basically a function of NDVI and LST. The Average SMI value of the rainfed area shows good correlation with the SPI 6 in the month of April with, R2 = 0.754 and P = 0.002. The results of the assessment show that agricultural drought was in its peak in 2006 (1.25%) based on the affected areas. However, widest spatial extent on agricultural drought rainfed rice plantation areas approximately 2.30% of the total rainfed area in 2005 (Nasrullah, S. et.al, 2009). New classification derived from linear regression shows 32.73% of total study area and 59.67% in rainfed areas was affected by drought. Thus, risk was estimated by drought hazard result of April 2006 and assumed vulnerability of the rice plantation areas equal to 1. In the test of deficit irrigation application, results shows 53.78% of the total rice plantation areas were exposed to different degrees of dryness. Yield varies at no applied irrigation and normal irrigation from zero to 6.975 tons per hectare in dry season, and from 4.2 to 6.975 tons per in wet season. Thus, it implies that rice is more sensitive to irrigation in dry season that in the wet season. Furthermore, 50% reduction on water requirement results to profitable yield.