Limitations to adjusting growing periods in different agroecological zones of Pakistan

CONTEXT: Climate change affects the timing and length of crop seasons. Adjusting sowing dates is a commonly recommended adaptation, but little is known about its efficacy in practice. OBJECTIVE: This study investigated farm-level adjustments to sowing and harvesting dates (i.e., the growing period) in response to shifts in meteorological crop seasons during the last 30 years. Impacts on yields and farmers' complementary adaptation strategies were also examined. METHODS: Using data from 287 farm households in four agroecological zones of the Indus Basin, Pakistan, we explored farmers' perceptions of shifts in seasons and adjustments in crop growing period. We verified these using meteorological station data on temperatures, precipitation and growing degree days. RESULTS AND CONCLUSIONS: At lower altitudes (irrigated plains and mid-hills), the summer crop season had lengthened and the winter season shortened, but in both seasons the growing period was shorter, due to higher temperatures. The summer growing period was shorter by 5 (±11) days on the irrigated plains, while there was no significant change in length of the summer growing period in the mid-hills. The winter growing period was shorter by 15 (±6) days on both the plains and in the mid-hills, which negatively impacted yields. As an adaptation strategy, changing sowing dates was only somewhat effective in preventing yield losses. Farmers adopted complementary strategies, but these brought additional costs. At higher altitudes (valleys and mountains), the frost period had shortened, resulting in longer summer and winter crop seasons, and longer growing periods. The summer growing period was extended by 7 (±4) days in the valleys and 10 (±6) days in the mountains, while the winter growing period was extended by 3 (±3) days in the valleys and 13 (±5) days in the mountains, positively impacting yields. Farmers' adjustments in sowing dates did not necessarily parallel to seasonal shifts, as farm decision-making also had to consider risks linked to climate variability and management limitations. For the future, farmers at lower altitudes indicated limited further scope for adjusting sowing and harvesting dates. SIGNIFICANCE: Our results contribute to a contextual understanding of farmers' responses to shifts in crop seasons. They indicate the need for adaptation planning to take advantage of extended growing periods in higher altitude zones, while supporting farmers in areas where seasonal shifts have negative impacts. Our findings furthermore indicate limits to adaptation in regions where agriculture is already challenged and provide suggestions for crop system-specific complementary measures.