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 dry season corn has now started in some areas of the country. Good to above normal yield is expected in Tuguegarao, Tayabas, Calapan, Romblon, Masbate, and Panay Island; while in Pto. Princesa, Mactan, Dumaguete, Zamboanga, Misamis Oriental and Bukidnon, no planting activities were done because of very low rainfall available in those areas during the November planting season. Standing newly-planted, lowland 2nd palay and dry season corn crops are in good condition in Baler, most of CALABARZON, Bicol Region, Catbalogan, Tacloban, Surigao del Sur and Surigao del Norte. In contrast, standing crops in Ilocos Sur, Ilocos Norte, Cagayan Valley, Cabanatuan, Casiguran, most parts of MIMAROPA, Panay Island, Mactan, and Zamboanga del Sur, experience moisture stress; while crops in Catarman were affected by water logging.

The weather systems that affected the country during the month were the Northeast (NE) Monsoon, Low Pressure Areas (LPAs), Tail-end of Cold Front (TECF), Easterlies, Inter-tropical convergence zone (ITCZ). No tropical cyclones had developed or entered in the Philippine Area of Responsibility (PAR).

Assessment of rainfall for the month showed that generally near to above normal rainfall conditions were experienced in most parts of Luzon, including most parts of Western and Eastern Visayas, Davao Region and SOCCSKSARGEN. The rest of Luzon, Central Visayas and most areas of Mindanao received way to below normal rainfall.


Lowland 2nd palay in Ilocos Sur and Ilocos Norte now in vegetative stage still suffered moisture stress due to very low moisture available during the month.
Harvesting of early-planted dry season corn has now started in Cagayan Valley. Yield is expected to be good despite the moisture deficiency during the month. Standing, late-planted lowland 2nd palay as well as the vegetating dry season corn has suffered from moisture stress.
Any farming activities related to planting rice and corn may not be done in any part of the region because of insufficient moisture available during the month.
Standing lowland 2nd palay planted in November suffered moisture stress in Cabanatuan and Casiguran, because of insufficient rainfall received during the month. It is also noted that December planted dry season corn in Casiguran also experienced moisture deficiency, but in Baler the standing rice and corn crops are faring well.
Harvesting of early-planted, dry season corn is ongoing in Tayabas; yield is expected to be good to normal because crops experienced good crops condition from planting to maturity. In a similar manner, outlook of dry-season corn and lowland 2nd palay is still good, although January rainfall is below normal but moisture is still sufficient for crops growth and development.
Harvesting of early-planted, dry-season corn had just begun in Calapan and Romblon; good to normal yield is projected due to sufficient moisture experienced by the crops during its critical stage of growth. Meanwhile, the standing dry season corn crops and the late-planted lowland 2nd palay in most parts of the region are now suffering from moisture deficiency.
Good weather and sufficient moisture available during the month favors the harvestable early- planted, dry season corn in Masbate; yield is expected to be near normal to above normal. Likewise, lowland 2nd palay as well as dry season corn in most parts of the region remain in good condition since soil moisture reserve is more than sufficient for crop growth and development.
Moisture supply is becoming inadequate for the newly-planted, lowland 2nd palay and the vegetating dry season corn in Mactan. It is because of the minimal rainfall received during the month.
Harvesting of early-planted dry season crops had just started in most parts of the region; good to near normal yield is anticipated because crops experienced positive condition throughout its growing period. On the other hand, standing rice and corn crops experienced moisture deficiency due to very minimal rainfall received during the month.
The newly-planted, lowland 2nd palay as well as the vegetating, dry-season corn continued to experience good crops condition in most parts of the region, same is true to the vegetating lowland 2nd palay planted in Catarman last November.
Crop condition of newly-planted, lowland 2nd palay as well as the vegetating dry-season corn is generally getting unfavorable. This is because of the very low rainfall received during the month.
No farming activities will be undertaken in the region due to the inadequate moisture during the month.
Good weather and ample amount of moisture available during the month favors all farming activities across the region.
Adequate rainfall received during the month is beneficial for farming activities in all parts of the region.
The flowering lowland 2nd palay in most parts of the region remain in good crop condition. The sufficient rainfall received during the month favored such crops. Likewise, standing late-planted, lowland 2nd palay and the vegetating dry season corn in Surigao del Norte and Surigao del Sur are faring well.
January rainfall has been inadequate for farming activities 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