This study investigates the impact of the northward/northwestward propagating 30-60-day mode of the boreal summer intraseasonal oscillation (BSISO) on the extreme rainfall events in the Philippines during the June-September (JJAS) season from 1979 to 2018. The Philippines domain is divided into the three latitudinal regions: Luzon region (13 -22 N), Visayas region (10 -13 N), and Mindanao region (5 -10 N) to account for the regional differences in the timing of extreme rainfall events. The probability density functions of JJAS rainfall are skewed towards higher values relative to the non-BSISO days in BSISO Phases 6-8, Phases 5-7, and Phases 4-6 over the Luzon, Visayas, and Mindanao regions, respectively, during which the probability of extreme rainfall events at the 95th percentile increases by as much as 80% in some stations in these regions. Further analyses of the large-scale circulation features show that the increase (decrease) in the probability of extreme rainfall events is associated with enhanced moisture convergence (divergence) induced by the cyclonic (anticyclonic) circulation anomalies of the BSISO and appearance of multiple tropical cyclones. About 36% of the total extreme rainfall events over the Luzon region are associated with TCs during Phases 7-8. On the other hand, TCs contribute by no more than 24% in all phases over the Visayas and Mindanao regions, indicating less TC influence in these regions. This study is the first attempt to clarify the impact of the BSISO on the extreme rainfall events in the Philippines.

To meet the growing demand for climate change information to guide national and local adaptation decision-making in the Philippines, the climate science and services community is producing an increasing volume of future climate data using a range of modelling approaches. However, there is a significant methodological challenge in how to best compare and combine information produced using different models and methods. In this paper, we present the landscape of climate model data available in the Philippines and show how multimodel, multi-method climate projections are being used and communicated to inform climate Climatic Change (2018) change policy and planning, focusing on the agriculture sector. We highlight the importance of examining and communicating methodological strengths and weaknesses as well as understanding the needs and capabilities of different user communities. We discuss the assessment of projections from different methods, including global and regional downscaled simulations, and discuss ways to summarise and communicate this information to stakeholders using coproduction approaches. The paper concludes with perspectives on how to best use an Bensemble of opportunity^to construct defensible, plausible and usable climate projections.

This paper presents a comprehensive analysis of the effect of urbanization on the surface air temperature (SAT) from 1951 to 2018 in the Philippines. The daily minimum temperature (Tmin) and daily maximum temperature (Tmax) records from 34 meteorological stations were used to derive extreme temperature indices. These stations were then classified as urban or rural based on satellite night‐lights. The results showed a significant difference in the SAT trends between urban and rural stations, indicative of the effect of urbanization in the country. Larger and more significant warming trends were observed in indices related to Tmin than those related to Tmax. In particular, the effects of urbanization were significant in the annual index series of Tmin, diurnal temperature range, minimum Tmin, percentage of days when Tmin was less than the 10th percentile (TN10p), percentage of days when Tmin was greater than 90th percentile (TN90p), and the number of coldest nights. The effects of urbanization were not as clear on the index series of maximum Tmax (TXx), minimum Tmax (TXn), percentage of days when Tmax was less than 10th percentile (TX10p), and the number of hottest days. The effects of urbanization on the annual series of extreme temperature indices were statistically significant at the 95% confidence level, with the exception of Tmax, TXn, TXx, TX10p, and the number of hottest days. Further analysis revealed that the effect of urbanization was the greatest during the DJF (December–January–February) season. These findings serve as a baseline study that focuses on the countrywide effect of urbanization on SAT trends in the Philippines.

This study investigates the climatological characteristics of the monsoon breaks during the southwest monsoon season (June–September) of the Philippines from 1979 to 2020. The monsoon break is defined as a period when the average rainfall across the eight western coast stations of the Philippines decreases below 5 mm·day−1 for at least three consecutive days. About 208 monsoon break events were identified, with 131 short‐ (3–4 days; 63% of the total monsoon break events), 71 medium‐ (5–9 days; 34%) and 6 long‐duration (≥10 days; 3%) monsoon break events. The short‐ and medium‐duration monsoon breaks were found to be more frequent during June and less frequent during August. Lag composite analyses of the time series of rainfall, low level zonal wind (UWND850hPa), vertically integrated moisture flux convergence (VIMFC) and mid‐tropospheric geopotential height (HGT500hPa) relative to the starting date of the monsoon break events show that the monsoon break is characterized by decrease in rainfall, weakening of westerly winds, increase in HGT500hPa and suppression of VIMFC over Luzon Island. Further analyses of the large‐scale circulation features show the appearance of an anticyclonic circulation over Luzon Island that suppresses the rainfall in the region and westward extension of the western North Pacific Subtropical High (WNPSH). The occurrence of the monsoon break events appears to be modulated by the 30–60‐day mode of the boreal summer intraseasonal oscillation (BSISO). About 39%, 55% and 82% of the short‐, medium‐ and long‐duration monsoon break events occur between Phases 1 and 4 during significant suppressed phases of the BSISO (i.e., amplitude >1), respectively. Convective activities and tropical cyclone activities are generally suppressed in these phases. The suppression of convective activities near the Philippines may facilitate the westward expansion of WNPSH, which further suppresses the rainfall and weaken the southwest monsoon.