Summer 2026 brought contrasting solar resource conditions across Asia as El Niño developed and the Western Pacific Subtropical High shifted farther north than normal, according to analysis using the Solcast API. The displaced high-pressure system brought more cloud and rainfall to Northeast China while supporting sunnier conditions across central parts of the country. Farther south, the transition towards El Niño, reinforced by a positive Indian Ocean Dipole, reduced cloud across eastern Indonesia and Papua New Guinea, although smoke limited irradiance gains in western Indonesia.
The northward shift of the Western Pacific Subtropical High created opposing irradiance conditions across China. This large, semi-permanent high-pressure system over the western Pacific helps determine the position of East Asia’s summer rain belt and the paths taken by tropical weather systems. In 2026, its northward position carried moist air and persistent rainfall into Northeast China and parts of Siberia, reducing irradiance by as much as 20%. The same shift contributed to flooding in Shenyang in early to mid-July and slowed the accumulation of GHI through the season.
Farther southwest, the high-pressure ridge suppressed cloud over Sichuan, Chongqing and Guizhou, lifting irradiance 20% to 25% above average. The Sichuan Basin was particularly notable. Its enclosed terrain typically supports frequent cloud and fog, giving the basin some of China’s lowest summer GHI based on the 2007-2025 average. Against this low climatological average, relatively small absolute variations produce large percentage anomalies, as is the case with the 25% anomaly this year.
Along southeastern China and across most of Mainland Southeast Asia, irradiance was around 5% to 10% below normal. Easterly winds on the southern side of the displaced high steered tropical systems westward, rather than allowing them to turn north. Tropical Storm Maysak (June 29-July 6) and Typhoon Narra (22-24 August) contributed cloud and rainfall along this corridor.
Farther south, the developing El Niño began to exert a clearer influence across Indonesia and neighbouring island regions, reducing the rising air that normally supports tropical cloud and rainfall. This effect was reinforced by a positive Indian Ocean Dipole, a difference in ocean temperatures across the Indian Ocean that commonly reduces rainfall near Indonesia during its positive phase. Eastern Indonesia and Papua New Guinea recorded irradiance 20% to 25% above average.
Western Indonesia experienced a smaller increase despite Indonesia recording its driest July since 1991. Fire hotspots in Sumatra and Kalimantan produced smoke during August, scattering and absorbing incoming sunlight and offsetting some of the irradiance increase expected from reduced cloud.
ECMWF SEAS5 forecasts indicate that above-normal irradiance will persist across Indonesia and the surrounding island region from September to November. The dry pattern associated with El Niño and the positive Indian Ocean Dipole extends beyond the usual end of the dry season in October, with no clear recovery associated with monsoon onset.
The forecast also indicates an early monsoon withdrawal over Mainland Southeast Asia. A strong positive anomaly over Northeast China and Korea in September is expected to weaken into a broader, less concentrated area of above-normal irradiance during October and November.
Solcast produces these figures by tracking clouds and aerosols at 1-2km resolution globally, using satellite data and proprietary AI/ML algorithms. This data is used to drive irradiance models, enabling Solcast to calculate irradiance at high resolution, with typical bias of less than 2%, and also cloud-tracking forecasts. This data is used by more than 350 companies managing over 350 GW of solar assets globally.
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