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


The standing, late-planted lowland palay as well as the vegetating, late-planted upland palay might be moderately affected by water-logging due to heavy rains brought by the strong southwest monsoon that was influenced by tropical cyclones.
The vegetating, late-planted upland palay and the standing, newly-planted lowland palay in the Batanes group of islands is faring well due to adequate moisture available during the month. While in Tuguegarao, July-planted, lowland palay experienced moisture stress.
Harvesting of upland 1st palay has begun across the region; yield is expected to be minimal because crops exposed to water-logging due to heavy rains brought by tropical cyclones that affected the country during maturing stage. The standing vegetating late-planted upland as well as the July-planted, lowland 1st palay might also be affected.
Harvesting of upland palay had just begun in Baler; good to normal yield is anticipated because crops were good condition during the critical stage of growth and development. The standing, vegetating late-planted upland palay experienced moisture stress due to insufficient moisture available during the month in the eastern parts of the region. While in the western part, particularly in Zambales and Nueva Ecija, the newly-planted, lowland palay and the vegetating, upland palay may be affected by water logging caused by the enhanced southwest monsoon.
Harvesting of upland 1st palay in Tayabas now started; good to normal yield is expected in the area due to well distributed moisture that was available from planting to maturity. The standing palay crops, however, might have experienced moisture stress due to excess rain. This available moisture, on the other hand, is sufficient for the vegetating, late-planted upland 1st palay and late-planted, lowland palay in Ambulong.
Harvesting of upland palay in Calapan has now begun: yield this season is expected to be good because crops were in good condition during the critical stage of growth. Standing upland and lowland 1st palay in the City might experience moisture stress because of the minimal rainfall in August. In contrast, standing palay crops in other parts of the region are faring well due to sufficient moisture available during the month.
Harvesting of lowland 1st palay in Albay had just started, good yield is anticipated because crops recovered from moisture stress and fared well until maturity. The standing, vegetating lowland palay in Catanduanes are still under moisture stress. On the other hand, the standing, lowland 1st palay in Camarines Norte are in good condition due to the sufficient moisture available during the month.
Farming activities that involves planting the late-planted 1st upland palay could not commence because of the insufficient moisture across the region
Harvesting of upland 1st palay had just begun across the region; good to normal yield is expected this season. Sufficient amount of rainfall received during the month is favorable for the standing, late-planted lowland 1st palay and upland, 1st palay across the region, they are now in good condition.
Harvesting of upland 1st palay had just started in Catbalogan and Tacloban; good yield is anticipated because crops experienced sufficient moisture condition during the critical stage of growth. Meanwhile, standing crops in these areas might suffer moisture stress because of the insufficient rainfall received during the month.
No harvestable crops are expected all throughout the region because of the insufficient amount of rainfall since June.
Harvesting of late-planted, upland palay in Bukidnon and Misamis Oriental is now in progress. Good to normal yield is anticipated in Bukidnon because sufficient moisture was available to the crops from planting to maturity. Meanwhile, in Misamis Oriental, below normal yield is expected because the crops suffered from moisture stress during their critical stage of growth. Standing late-planted, lowland palay were also affected in Misamis Oriental, however, crops in Bukidnon are faring well.
No harvest of late-planted, upland palay may be expected across the region since no farming activities commenced due to the minimal amount of rainfall received last June.
Insufficient rainfall received since June resulted to the postponement of farming activities for rice and corn across the region.
Harvesting of late-planted, lowland 1st palay in Surigao del Norte had commenced; good yield is anticipated because crops recovered from moisture stress. The crops suffered from moisture stress during the critical stage of growth, but in the 1st and 2nd decade of the month (from flowering to maturity) the crops were able to recover.
Standing July-planted, lowland 1st palay are faring well because of the sufficient moisture available during the month.

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