Climate Change Chart of Tehran, Iran

Overview of climate changes

Temperature changes

Across calendar months, the unweighted mean difference in monthly mean temperature was +1.74 °C compared with the earlier reference period; this summarizes the month-by-month averages and is not a day-weighted annual mean or a statement that every month warmed. The largest monthly increase was in March, with a difference of +3.34 °C. By contrast, November had the largest monthly decrease, at -0.01 °C. These are changes in monthly mean temperature, not daytime maximum temperatures.

Changes in rainfall

Averaged across calendar months, mean daily rainfall had an unweighted difference of +0.10 mm/day; this is a summary of monthly means, not a day-weighted annual average or a monthly total. The largest monthly increase occurred in November, at +0.59 mm/day, while the largest decrease was in May, at -0.24 mm/day. These daily-mean differences describe contrasts between the reference periods and do not imply that rainfall changed in the same direction in every month.

Changes in sunshine duration

Mean daily sunshine duration was lower on average across calendar months, with an unweighted difference of -0.37 hours/day compared with the earlier reference period; the figure summarizes monthly means rather than a day-weighted annual average. The largest monthly decrease was in April, where the difference was -0.86 hours/day. This monthly contrast does not establish that sunshine duration declined in every month.

Changes in snowfall

Mean daily snowfall had an unweighted difference of -0.19 mm/day when the monthly means are averaged across calendar months, rather than a day-weighted annual average or monthly total. The largest monthly decrease was in December, at -1.16 mm/day, while the largest increase was in November, at +0.37 mm/day. The contrast between these monthly differences shows why the overall mean should not be taken to describe every month; these figures concern daily means, not snowfall totals.