ASSESSMENT OF THE POTENTIAL EFFECTS OF LONGTERM TEMPERATURE AND PRECIPITATION TRENDS ON IRRIGATION WATER REQUIREMENTS IN ÇANAKKALE, TÜRKIYE

20TH INTERNATIONAL ISTANBUL SCIENTIFIC RESEARCH CONGRESS, İstanbul, Türkiye, 28 - 30 Eylül 2026, ss.1155-1164, (Tam Metin Bildiri)

Long-term warming can increase crop water demand even when precipitation does not exhibit a

comparable decline. This study quantified how observed temperature and precipitation trends have

translated into maize net irrigation water requirement (NIR) in Çanakkale, northwestern Türkiye, over

1929–2025. Monthly mean temperature and precipitation from Turkish State Meteorological Service

station 17112 were quality-controlled and completed where necessary using calendar-month long-term

means. Monotonic trends were evaluated with the Mann–Kendall test and Sen’s slope estimator.

Reference evapotranspiration (ET0) was calculated with a simplified temperature-based Blaney–Criddle

formulation, while maize crop coefficients and a fixed 160-day crop calendar (1 May–7 October) were

adopted from TAGEM-SuET. Crop evapotranspiration (ETc), effective precipitation, and NIR were

then calculated consistently for all 97 years. Annual mean temperature increased by 0.128 °C decade−1

(conventional Mann–Kendall p<0.001), whereas annual precipitation showed a small, non-significant

decline of 2.74 mm decade−1 (p=0.622). During the maize growing season, temperature, ET0, and ETc

increased by 0.159 °C, 3.68 mm, and 3.31 mm decade−1, respectively (conventional Mann–Kendall

p<0.001), while growing-season precipitation and effective precipitation had no significant trends. NIR

increased significantly by 2.80 mm decade−1 (p=0.009), from an average of 735.86 mm in 1929–1958

to 753.70 mm in 1996–2025. The mid-season stage accounted for approximately 54% of long-term NIR,

with July and August together contributing about 62%. Taken together, the long-term rise in NIR is

more consistent with increasing evaporative demand than with a persistent decline in seasonal

precipitation. These findings support temperature-sensitive irrigation planning under Mediterranean

conditions.