Agricultural burning in Southeast Asia often creates a haze. In 2003 Thailand ratified the ASEAN Agreement on Transboundary Haze Pollution to reduce the haze from forest fires, but issues throughout the region are still common.[15] Wildfires are started by local farmers during the dry season in northern Thailand for a variety of purposes,[16][17] with February and March as the two months when conditions are at their worst.[18][19] In research conducted between 2005 and 2009 in Chiang Mai, average PM10 rates during these months were found to be well above the country's safety level of 120 μg/m3,[20] peaking at 383 μg/m3 on 14 March 2007.[21] They are the main cause of the intense air pollution in the Thai highlands[22] and contribute to the floods in the country by completely denuding the undergrowth of the woods.[23] The dry forest soil leads to lower water intake for trees to extract when the rains arrive