Wet and dry extremes in Quito (Ecuador) since the 17th century

Wet and dry extremes in Quito (Ecuador) over the last 400 years are studied using two sources of information: the longest available instrumental rainfall series in northern South America (1891-2015) and the rogation ceremonies recorded in the Chapter Acts of Quito (1600-1822). The rogation ceremonies present a seasonal distribution that is related to the crops and to the typical distribution of rainfall over the year. August was the month with most pro serenitate rogations because farmers needed dry conditions for harvest, whereas excess rainfall at this time would lead to rotting and loss of the harvest. The pro pluvia rogations were markedly more frequent during January and February when farmers needed rain for sowing. This relationship between climate and farming activities makes Quito's rogations a good proxy for drought and extreme wet conditions during January-February-March (JFM) and wet conditions during June-July-August (JJA). Standardized precipitation index (SPI) was computed for the instrumental period. The 3-month SPI showed a significant linear trend over the last 125 years (-0.4 per decade, p = 0.009). The five wettest periods were 1651-1657, 1663-1669, 1913-1919, 1950-1956, and 1981-1985. Droughts have intensified in frequency and length since the middle of the 20th century. The most important drought periods were 1692-1701, 1718-1723, 1976-1980, 1990-1993, and 2001-2006. The severest drought during the last 400 years occurred in 1692-1701 when a great famine devastated Quito and affected most of the central Andes.