Impact Assessment for Agriculture

The Impact Assessment and Applications Section (IAAS) of Climatology and Agrometeorology Division (CAD) regularly issue this monthly/bulletin which will provide users such as food security managers, economic policy makers, agricultural statisticians and agricultural extension officials with qualitative information on the current and potential effects of climate and weather variability on rainfed crops, particularly rice and corn. This bulletin, entitled “Climate Impact Assessment for Agriculture in the Philippines”, represents a method for converting meteorological data into economic information that can be used as supplement to information from other available sources.

For example, an agricultural statistician or economist involved in crop production and yield forecast problems can combine the assessment with analysis from area survey results, reports on the occurrence of pests and diseases, farmers’ reports and other data sources.

The impact assessments are based on agroclimatic indices derived from historical rainfall data recorded for the period 1951 to the present. The indices, expressed in raw values percent of normals and percentile ranks, together with real time meteorological data (monthly rainfall, in percent of normal), percent of normal cumulative rainfall, as well as the occurrence of significant event such as typhoons, floods and droughts are the tools used in the assessment of crop performance. Crop reports from PAGASA field stations are also helpful.

The narrative impact assessment included in the bulletin depicts the regional performance of upland, 1st lowland and 2nd lowland palay; and dry and wet season corn crops, depending on the period or the season. Tabulated values of normal rainfall and generalized monsoon and yield moisture indices are provided for ready reference. Spatial analysis of rainfall, percent of normal rainfall and the generalized monsoon indices in percentile ranks are also presented on maps to help users visualize any unusual weather occurring during the period. The generalized monsoon indices in particular, are drought indicators; hence, the tables (see Appendices) together with the threshold values can be used in assessing drought impact, if there are any. It also helps assess any probable crop failure.

It is hoped therefore that this bulletin would help provide the decision-makers, planners and economist with timely and reliable early warning/information on climatic impact including the potential for subsistence food shortfalls, thereby enabling them to plan alternate cropping, if possible, food assistance strategies/mitigation measures to reduce the adverse impact of climate and eventually improve disaster preparedness.

Impact assessment for other principal crops such as sugarcane and coconut, for energy and for water resources management, are from time to time will be included in the forthcoming issues of this bulletin.

The IAAS of CAD will appreciate suggestions/comments from end-users and interested parties for the improvement of this bulletin.

Definition of Terms
The Generalized Monsoon Index (GMI) helps determine the performance of the rains during the season and serves as a good indicator of potential irrigation supplies. It is a tool used to assess rainfed crops.

The GMI for the southwest monsoon (GMIsw) in an area during June to September is defined as follows:
GMIsw = W6P6 + W7P7 + W8P8 + W9P9

The GMI for the northeast monsoon (GMIne) in an area during October to January is defined as:
GMIne = W10P10 + W11P11 + W12P12 + W1P1


W = weight coefficient of monthly rainfall for the season;
P = rainfall amount in the ith month
(i = 1 for January, 2 = for February, etc.)

The Yield Moisture Index (YMI) is a simple index that helps the users assess agroclimatic crop conditions during the crop season. The YMI for a particular crop is defined as follows:
n YMI =  [Pi Ki] i


i = crop stage (1 = planting/transplanting,
2 = vegetative, 3 = flowering, 4 = maturity, etc.)
n = total no. of crop stages;
P = rainfall during the ith crop stage; and
K = appropriate crop coefficient for the ith crop stage.

Tentatively, the threshold values of categories of indices for interpretation being adopted for both YMI and GMI are as follows:

> 80 Potential for Flood Damage
41 - 80 Near normal to above-normal crop condition
21 - 40 Moderate drought impact with reduced yield
11 - 20 Drought impact with major yield losses
< 10 Severe drought impact with crop failure and potential food shortages



Harvesting of early-planted wet season corn has started in most parts of the country; good to normal yield is expected in Casiguran, most of CALABARZON, Camarines Norte, Eastern Visayas, and most of CARAGA Region. Contrastingly, below normal yield is anticipated in most provinces of Bicol Region and in Butuan. Land preparation and planting of dry season corn has now started in some parts of the country.

General assessment for the month of April shows that way below to below normal rainfall conditions were experienced in most parts of Northern and Southern Luzon, some parts of Visayas, and Northern Mindanao. Meanwhile, near to above normal rainfall were received in most areas of Central Luzon, Visayas, and Mindanao.

The weather systems that affected the country during the month were the Northeast Monsoon, tail end of cold front, low-pressure areas (LPAs), easterlies, ridge of high-pressure area (HPA). Termination of the northeast monsoon signifies the start of warm and dry season in major areas of the country...


The rainfall amount during the month is still inadequate for any farming activity across the region.
The moisture available in the region is insufficient for planting activities related to rice and corn.
Farming activities related to planting rice and corn are not possible because of the scarcity of moisture available during the month.
Sun-drying and stocking of post harvested late-planted lowland 2nd palay in Baler and Casiguran is in the final stage which was favored by the previous weather and climate conditions.
Insufficient rainfall received during the month hampered all farming activities related to planting dry-season corn. In Infanta and in other neighboring areas across the region.
The minimal amount of rainfall received during the month is unfavorable for any planting activity related to rice and corn throughout the region.
Farming activities related to planting dry season corn are all hampered across the region due to the insufficient moisture during the month.
Due to the minimal rainfall received during the month, farming activities cannot be undertaken throughout the region.
Because of the minimal rainfall received during the month, farming activities are hindered in all parts of the region.
Farming activities related to planting rice and corn are not possible across the region due to the scarcity of moisture available during the month.
Scarcity of moisture is still prevalent across the region, thus any farming activity related to planting rice and corn cannot be undertaken during the month
Insufficient moisture brought by minimal amount of rainfall received during the month hindered any farming activity to be done in any part of the region.
Since January until the current month, the rainfall received across the region remains insufficient for farming activities related to rice and corn.
Moisture remains inadequate throughout the region, hence farming activities are hindered during the month.
Harvesting of early planted wet season corn have just started in Surigao del Sur and Surigao del Norte; near-normal to above-normal yield is expected because crops remained in good condition from planting to maturity. Likewise, the sufficient moisture available during the month favors planting of dry season corn across the region
Moisture remains insufficient during the month, that is why no farming activity related to planting dry season corn is possible across the region.

Ten Day Rainfall Distribution

Monthly Rainfall Distribution

Generalized Moonsoon Index

Tropical Cyclone

No Active Tropical Cyclone

Actual Rainfall and Potential Evapotranspiration


For Particulars, please contact:


Impact Assessment and Applications Section (IAAS)

Climatology and Agrometeorology Division (CAD)


Telefax No.: 434-58-82