The project focuses on analysing the Climate data for DWD Station: Hamburg Fuhlsbüttel for the period 1936-2025.
The source for this data is in the following link :- opendata.dwd.de/climate_environment/CDC/observations_germany/climate/daily
- Temperature Analysis
- Precipitation Analysis
- Computation of Drought Indices and Analysis: a) Reconnaissance Drought Index (RDI) b) Standarized Precipitation Evapotranspitation Indexc (SPEI) c) Standardized Precipitation Index (SPI)
I first perform Temperature analysis for Hamburg Fuhlsbüttel
Annual Temperature Trend (1936–2024)
📊 Decadal Temperature (Bar Plot)
📉 Decadal Temperature Trends (Line Plot)
🔥 Heatwave Intensity Trend (1990–2024)
🌡️ Maximum Daily Exceedance in Heatwaves (1990–2024)
🔁 Annual Number of Heatwave Events (HWMId, 1990–2024)
🗓️ Julian Day of Peak Heatwave Intensity
📅 Frequency of Heatwave Peak Months (1990–2024)
📆 Peak Months by Decade
🧮 Heatwave Frequency per Climatology Period
📊 Frequency of Heatwave Events (Tmax ≥ 28°C, ≥3 Days)
🐢 Top 10 Slowest Heatwave Declines
⏳ Top 10 Longest Duration Heatwave Events
📌 Top 10 Heatwaves by Maximum Intensity
Precipitation Trend (1936-2025) ####
.png)
Precipitation Concentration Index (PCI)
-
Overall Stability: PCI values consistently range between ~9.0-13.5 over 89 years Mean appears stable around 10.5-10.6 (moderate concentration) No significant long-term trend (black LOESS line is relatively flat)
-
Temporal Patterns: 1940s-1950s: Higher variability and more frequent spikes above 13 1960s-1980s: More stable period with fewer extreme values 1990s-2020s: Return to higher variability, similar to 1940s-1950s
-
Climate Implications: Hamburg maintains moderate seasonal precipitation concentration throughout the recordNo evidence of increasing concentration due to climate changeThe variability suggests natural climate oscillations rather than systematic change
-
Extreme Years: Several years show PCI >13 (irregular distribution): notably in 1940s, 1960s, and 2000s-2010sThese likely represent years with particularly wet or dry seasons German Climate Context Analysis:Regional Climate Influences: Hamburg, being in northern Germany near the North Sea, is particularly influenced by Atlantic weather systems and the North Atlantic Oscillation (NAO). The cyclical peaks you see (1999, 2011, 2018) likely correspond to periods when these Atlantic systems created more concentrated precipitation patterns.Seasonal Concentration: In Germany's temperate oceanic climate, high PCI values often indicate: Wet winters followed by dry summers (or vice versa).Clustering of precipitation into fewer, more intense events.Potential impacts from blocking high-pressure systems over Central Europe
The increasing volatility after 2010 aligns with observed climate change impacts in Germany, including: More frequent extreme weather events,Shifts in seasonal precipitation patterns.Increased likelihood of both drought periods and heavy rainfall events Recent Trends (2020-2024): The declining trend toward 2024 might reflect:Changes in storm track patterns affecting northern Germany.Potential shifts in the timing or intensity of Atlantic low-pressure systems.Regional impacts of broader European climate variability Agricultural/Hydrological Implications: For Hamburg and northern Germany, these PCI fluctuations have significant implications for water management, agriculture, and flood risk - particularly given the region's importance for German agriculture and its proximity to major river systems.The data suggests Hamburg has experienced increasingly variable precipitation concentration patterns, which is consistent with climate projections for Northern European regions.
Spring Season
Summer Season
Fall Season
Winter Season
Comparison of Period 1936:1979 & 1980:2025 for Winter Season
1980 Breakpoint Analysis: Mean increase: 30.8mm (166mm → 197mm) Percentage increase: 18.6% Median increase: 38mm (164mm → 202mm) Variability: Standard deviation increased from 60.3mm to 67.2mm
1990 Breakpoint Analysis: Mean increase: 27.3mm (171mm → 198mm) Percentage increase: 16.0% Median increase: 23mm (175mm → 198mm) Variability: Standard deviation increased from 59.5mm to 71.2mm
Key observations: Both breakpoints show substantial increases (~16-19%), confirming the trend is robust The 1980 breakpoint shows a slightly larger absolute increase (30.8mm vs 27.3mm), suggesting the trend started earlier but was more gradual The 1990 breakpoint shows the trend is more concentrated in the recent period (36 years vs 46 years) Increased variability in both cases - winters are not only getting wetter on average, but also more variable (higher standard deviation) The medians follow similar patterns to the means, indicating this isn't driven by a few extreme years
Climate implications: An 18% increase in winter precipitation over ~45 years is climatologically significant The increased variability suggests more extreme wet and dry winters This aligns with climate projections for Northern Europe showing wetter winters
This is a clear signal of changing winter precipitation patterns at Hamburg Fuhlsbüttel!
Focus is on long term trend, so using monthly series of drought indices with a frequency of 12,36,24,48 . The plots shows that last decade has witnesses increase in temperature and on the other decrease in precipitation. This makes the situation worse in future as with further increase in temperature the weather will become more dry and will result in a further decrease in precipitation resulting in a severe drought.
The Reconnaissance Drought Index (RDI) is a meteorological drought index that assesses drought severity by comparing precipitation to potential evapotranspiration (PET). It's a valuable tool for understanding water availability and is often used in agriculture and water resource management.
RDI 12 monthly Index
RDI 24 monthly Index
RDI 36 monthly Index
RDI 48 monthly Index
Scale-Dependent Drought Evolution:
12-month: High variability, frequent short droughts 24-month: Intermediate persistence, moderate severity increases 36-48 month: Dramatic modern intensification of severe droughts
Temporal Transition Patterns:
1959-1960: Historic extreme drought cluster across 12-24 month scales 1990s: Major wet period peak (especially May 1995) 2018-2022: New drought era with unprecedented long-term severity
Modern Climate Signal Strength by Scale:
12-month: Moderate increase (6.8% → 7.8% severe drought) 24-month: Slight decrease (6.2% → 5.6% in full period) 36-month: Nearly doubled (3.3% → 6.1% severe drought) 48-month: Tripled (2.7% → 8.2% severe drought)
Most Concerning Finding: The 48-month scale shows the strongest climate change signal, indicating that multi-year drought persistence has fundamentally changed in Hamburg's climate system.
Hydrological Implications:
Short-term droughts (12-24 months): Affect seasonal water management Long-term droughts (36-48 months): Threaten groundwater recharge, ecosystem resilience, and agricultural sustainability The tripling of severe long-term droughts represents a major shift in regional water security
This analysis clearly shows that while short-term drought variability has increased moderately, the most dramatic change is in sustained multi-year drought conditions - exactly the type that poses the greatest challenge to water resources and ecosystem adaptation.
| Time Scale | Period | Drought Conditions | Severe Drought | Wet Events | Key Extreme (Dry) |
|---|---|---|---|---|---|
| 12-month | 1936–1989 | 23.6% | 6.8% | 31.7% | Oct 1959 (−3.9) |
| 1990–2025 | 28.2% | 7.8% | 27.1% | Jan 2019 (−3.0) | |
| 24-month | 1936–1989 | 29.6% | 6.2% | 33.3% | Jul 1960 (−2.7) |
| 1936–2025 | 32.9% | 5.6% | 31.5% | Jul 1960 (−2.75) | |
| 36-month | 1936–1989 | 36.1% | 3.3% | 33.4% | Jul 1940 (−2.0) |
| 1990–2025 | 37.2% | 6.1% | 29.2% | Jan 2021 (−2.9) | |
| 48-month | 1936–1989 | 36.1% | 2.7% | 27.6% | Jul 1941 (−1.85) |
| 1990–2025 | 36.9% | 8.2% | 27.1% | Jan 2022 (−2.7) |
| Scale | Period | Tau | Z-statistic | p-value | Trend Direction | Significance |
|---|---|---|---|---|---|---|
| 12-month | 1936–2025 | +0.0232 | 1.133 | 0.2572 | Slight Increase | ✗ |
| 24-month | 1936–2025 | +0.0353 | 1.711 | 0.0871 | Mild Increase | • |
| 36-month | 1936–2025 | +0.0434 | 2.093 | 0.0364 | Moderate Increase | ✓ |
| 48-month | 1936–2025 | +0.0528 | 2.534 | 0.0113 | Moderate Increase | ✓✓ |
| 12-month | 1936–1989 | +0.2098 | 7.920 | < 2.4e-15 | Strong Increase | ✓✓✓ |
| 24-month | 1936–1989 | +0.3233 | 12.088 | < 2.2e-16 | Strong Increase | ✓✓✓ |
| 36-month | 1936–1989 | +0.3839 | 14.215 | < 2.2e-16 | Strong Increase | ✓✓✓ |
| 48-month | 1936–1989 | +0.4417 | 16.194 | < 2.2e-16 | Strong Increase | ✓✓✓ |
| 12-month | 1990–2025 | -0.1626 | -5.008 | 5.49e-07 | Moderate Decrease | ✓✓✓ |
| 24-month | 1990–2025 | -0.2820 | -8.678 | < 2.2e-16 | Strong Decrease | ✓✓✓ |
| 36-month | 1990–2025 | -0.4383 | -13.497 | < 2.2e-16 | Strong Decrease | ✓✓✓ |
| 48-month | 1990–2025 | -0.5629 | -17.337 | < 2.2e-16 | Very Strong Decrease | ✓✓✓ |
Interpretation 1936–1989: All time scales show strong positive trends — conditions became wetter or less drought-prone.
1990–2025: Clear negative trends — longer scales (36, 48 months) show increasingly severe and prolonged drought conditions.
1936–2025: Full-period trends are mild and mixed — overall signal is weaker due to opposite trends in sub-periods.
Climatic Moisture Variability in Hamburg Fuhlsbüttel (1936–2025)
This analysis explores the Standardized Precipitation Evapotranspiration Index (SPEI) at multiple timescales (12, 24, 36, and 48 months) across two time periods:
- Historical Baseline: 1936–1989
- Recent Period: 1990–2025
| Scale | Period | Moderate Dry (%) | Severe Drought (%) | Extreme Drought (%) | Wet Events (%) | Wettest Event | Driest Event |
|---|---|---|---|---|---|---|---|
| SPEI-12 | 1936–1989 | 7.06 | 3.92 | 2.98 | 15.9 | May 1981 (2.3) | Mar 1960 (-3.02) |
| 1990–2025 | 10.35 | 4.71 | 2.35 | 19.5 | Aug 2002 (2.35) | Apr 2019 (-2.74) | |
| SPEI-24 | 1937–1989 | 9.92 | 4.64 | 1.92 | 16.6 | Nov 1981 (2.17) | Jul 1960 (-2.4) |
| 1990–2025 | 12.94 | 3.29 | 1.41 | 18.6 | Apr 1995 (2.37) | Jan 2020 (-2.24) | |
| SPEI-36 | 1938–1989 | 13.05 | 4.4 | 0.00 | 18.1 | May 1983 (2.12) | May 1978 (-1.97) |
| 1990–2025 | 7.53 | 4.71 | 2.59 | 13.4 | Sep 1995 (2.33) | Apr 2021 (-2.88) | |
| SPEI-48 | 1939–1989 | 14.31 | 3.16 | 0.00 | 21.3 | Oct 1981 (1.99) | Jun 1941 (-1.9) |
| 1990–2025 | 6.59 | 6.35 | 3.29 | 16.0 | Apr 1995 (2.2) | Jan 2022 (-2.73) |
- Drought severity increased post-1990, with more persistent and extreme droughts especially in the 36- and 48-month SPEI.
- Wet events dominated the earlier period (1936–1989), particularly in the early 1980s.
- Post-2000, the frequency of wet events decreased, while multi-year droughts increased in length and intensity.
- Recent extremes (e.g., Jan 2022, Apr 2021) point toward increasing climatic water deficits likely due to rising temperatures and evapotranspiration.
📌 Source: Deutscher Wetterdienst (DWD)
Statistical trends in SPEI indices were tested using the Mann–Kendall non-parametric test.
| SPEI Scale | Period | τ (Kendall’s Tau) | Z-Statistic | p-value | Trend Direction | Significance |
|---|---|---|---|---|---|---|
| SPEI-12 | 1936–1989 | +0.201 | +7.58 | 3.48e-14 | Increasing | ✅ Highly Significant |
| 1990–2025 | −0.153 | −4.72 | 2.31e-06 | Decreasing | ✅ Highly Significant | |
| SPEI-24 | 1936–1989 | +0.315 | +11.78 | < 2.2e-16 | Increasing | ✅ Highly Significant |
| 1990–2025 | −0.269 | −8.29 | < 2.2e-16 | Decreasing | ✅ Highly Significant | |
| SPEI-36 | 1936–1989 | +0.376 | +13.92 | < 2.2e-16 | Increasing | ✅ Highly Significant |
| 1990–2025 | −0.411 | −12.66 | < 2.2e-16 | Decreasing | ✅ Highly Significant | |
| SPEI-48 | 1936–1989 | +0.432 | +15.86 | < 2.2e-16 | Increasing | ✅ Highly Significant |
| 1990–2025 | −0.535 | −16.47 | < 2.2e-16 | Decreasing | ✅ Highly Significant |
- There is a clear reversal in trend direction between the two periods.
- Earlier decades (1936–1989) were characterized by gradual wetting, whereas
- Recent decades (1990–2025) show a marked drying pattern, especially in long-term moisture balance (SPEI-36, SPEI-48).
📌 Conclusion The analysis of the Standardized Precipitation Evapotranspiration Index (SPEI) across multiple time scales (12, 24, 36, and 48 months) for Hamburg Fuhlsbüttel reveals a distinct climatic shift around 1990. During the historical period (1936–1989), SPEI trends consistently increased, indicating a gradual improvement in climatic moisture conditions and reduced drought stress. However, post-1990, all SPEI time scales exhibit significantly negative trends, reflecting a transition toward drier conditions. This reversal is most pronounced at the longer time scales (SPEI-36 and SPEI-48), suggesting the emergence of persistent, multi-year droughts likely driven by increased evapotranspiration and reduced moisture availability. The Mann–Kendall trend tests confirm these findings with highly significant results (p < 0.001), underscoring a long-term hydroclimatic drying trend in the region. These results highlight the need for proactive water resource planning and climate adaptation strategies to address escalating drought risk in the decades ahead.
PLOTS FOR SPI INDEX FOR SCALE 12,24,36,48 MONTHLY
| SPI Scale | Period | Moderate Dry (%) | Severe Drought (%) | Extreme Drought (%) | Wet Events (%) | Wettest Event | Driest Event |
|---|---|---|---|---|---|---|---|
| 12-Month | 1936–1989 | 6.44 | 3.77 | 3.92 | 11.6 | May 1981 (3.02) | Dec 1959 (−3.48) |
| 12-Month | 1990–2025 | 4.47 | 2.35 | 3.76 | 21.2 | Apr 1994 (2.58) | Sep 1996 (−3.55) |
| 24-Month | 1936–1989 | 9.92 | 7.04 | 1.60 | 12.0 | Nov 1981 (2.55) | Jul 1960 (−2.74) |
| 24-Month | 1990–2025 | 4.00 | 1.65 | 1.41 | 21.4 | Apr 1995 (3.2) | Apr 1997 (−2.76) |
| 36-Month | 1936–1989 | 15.33 | 6.04 | 0.33 | 12.1 | May 1983 (2.71) | Jun 1954 (−2.14) |
| 36-Month | 1990–2025 | 3.06 | 2.35 | 0.47 | 23.5 | Sep 1995 (3.36) | May 1998 (−2.1) |
| 48-Month | 1936–1989 | 16.81 | 3.99 | 1.16 | 12.0 | Jun 1983 (2.26) | Mar 1960 (−2.22) |
| 48-Month | 1990–2025 | 5.41 | 1.18 | 0.00 | 20.9 | Apr 1995 (3.2) | Jan 2022 (−1.98) |
The Standardized Precipitation Index (SPI), calculated over 12-, 24-, 36-, and 48-month time scales, reveals distinct patterns across two climate periods:
1936–1989: SPI exhibits a significant positive trend across all time scales (Kendall’s τ ranging from 0.13 to 0.29).
This indicates a gradual shift toward wetter conditions, particularly noticeable in the 36- and 48-month scales.
Extreme drought events, while present, were infrequent and short-lived, especially on longer time scales.
Overall, this period reflects a climatic phase of stable or increasing precipitation in Hamburg.
1990–2025: SPI trends reverse sharply, with significant negative trends at 24-, 36-, and 48-month scales (τ = −0.12 to −0.28).
Short-term SPI-12 shows a marginally decreasing trend, though more frequent wet events appear at this scale.
Despite the visual impression of "wetness" in some SPI plots, the long-term drying signal becomes prominent in the 36- and 48-month SPI.
The contrast between wet and dry phases post-1990 highlights a more variable climate, where wet periods are punctuated by increasingly intense droughts.
Interpretation Caveat: SPI is based solely on precipitation. It does not account for temperature-driven evapotranspiration, which has risen significantly in recent decades. As such, SPI may underestimate drought risk under warming conditions, especially in humid temperate regions like Hamburg.
🔹 SPI-12 (Short-Term Droughts and Wet Spells) 1936–1989: Mildly increasing trend (τ = 0.138), with moderate droughts and wet events occurring periodically.
1990–2025: Trend reverses (τ = −0.059, marginal), but wet events nearly double (11.6% → 21.2%).
Interpretation: The SPI-12 reveals an increase in short-term wet anomalies post-1990, suggesting intermittent heavy precipitation, even as droughts remain significant.
🔹 SPI-24 (Mid-Term Climatic Fluctuations) 1936–1989: Strong wetting trend (τ = 0.234), indicating consistently favorable precipitation.
1990–2025: Significant drying trend (τ = −0.120), with severe drought events becoming more extreme.
Interpretation: The 24-month SPI exposes a clear shift toward hydroclimatic stress in the recent period, despite short-term rainfall episodes.
🔹 SPI-36 (Long-Term Moisture Conditions) 1936–1989: Highly significant wetting trend (τ = 0.264), with long wet periods dominating the climate.
1990–2025: Strong reversal (τ = −0.198), with increased frequency and persistence of drought.
Interpretation: SPI-36 highlights emerging long-term drought conditions, which are not apparent in short-term SPI scales.
🔹 SPI-48 (Multi-Year Climate Stress) 1936–1989: Very strong positive trend (τ = 0.291), aligned with decades of stable water balance.
1990–2025: Marked drying trend (τ = −0.281), the strongest negative signal among all SPI scales.
Interpretation: The SPI-48 reveals systemic drying, possibly related to cumulative effects of climate warming and shifting precipitation patterns. No extreme wet events have been observed in the recent decades.
📎 Key Takeaway While SPI initially suggested increased wetness in post-1990 Hamburg, longer time scales (24–48 months) reveal a strong drying signal. This confirms that short-term rainfall events may mask underlying multi-year drought trends. SPI’s exclusive reliance on precipitation also means it does not reflect increased evapotranspiration due to rising temperatures, unlike SPEI or RDI.
| SPI Scale | Period | Kendall’s Tau | Trend (M-K Test) |
|---|---|---|---|
| 12-Month | 1936–1989 | 0.138 | ↑ Significant |
| 12-Month | 1990–2025 | -0.059 | ↓ Marginal |
| 24-Month | 1936–1989 | 0.234 | ↑ Significant |
| 24-Month | 1990–2025 | -0.120 | ↓ Significant |
| 36-Month | 1936–1989 | 0.264 | ↑ Significant |
| 36-Month | 1990–2025 | -0.198 | ↓ Significant |
| 48-Month | 1936–1989 | 0.291 | ↑ Significant |
| 48-Month | 1990–2025 | -0.281 | ↓ Significant |
Climate data analysis for Hamburg Fuhlsbüttel reveals a clear hydrological regime shift after 1990, with drought indices (RDI, SPEI, SPI) showing a transition from consistently wetting trends (1936-1989) to intensifying multi-year drought conditions, particularly severe at 36-48 month timescales. The computed indices demonstrate that while short-term precipitation variability has increased, the most significant finding is the tripling of persistent drought frequency, indicating a fundamental change in the region's long-term water balance
R has been extensively used for the whole analysis, visualiaztion.